Detector, image forming apparatus, reading apparatus, and adjustment method

ABSTRACT

A detector includes a light source to irradiate an object with light, a sensor to image a first pattern and a second pattern formed on the object with the light irradiated by the light source to generate image data, the first pattern and the second pattern imaged by the sensor at different times, and a circuit to control the light source to adjust a light quantity of the light according to a type of the object and irradiate the object with the light quantity adjusted according to the type of the object, and calculate a relative position of the object between the first pattern and the second pattern.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based on and claims priority pursuant to 35U.S.C. § 119(a) to Japanese Patent Application No. 2017-117250, filed onJun. 14, 2017, and Japanese Patent Application No. 2018-089536, filed onMay 7, 2018, in the Japan Patent Office, the entire disclosure of eachof which are hereby incorporated by reference herein.

BACKGROUND Technical Field

Aspects of the present disclosure relate to a detector, an image formingapparatus, a reading apparatus, and an adjustment method.

Related Art

There is an image forming method that performs various types ofprocesses using an inkjet head (print head). For example, there is animage forming method that discharges ink from a print head (so-calledinkjet method). Further, there is a method to improve an image qualityof an image formed on an object in the image forming method.

For example, the method moves the print head to improve the imagequality. Specifically, the method uses a sensor to detect a positionchange of the object such as a web in a lateral direction in acontinuous sheet printing system. Then, the method moves the print headin the lateral direction to compensate the position change of the object(web) detected by the sensor.

Further, there is a method that images (captures) images atpredetermined two places and calculates a moving speed of the objectfrom correlation between the captured images.

SUMMARY

In an aspect of this disclosure, a detector includes a light source toirradiate an object with light, a sensor to image a first pattern and asecond pattern formed on the object with the light irradiated by thelight source, the first pattern and the second pattern imaged by thesensor at different times, and a circuit to control the light source toadjust a light quantity of the light according to a type of the objectand irradiate the object with the light quantity adjusted according tothe type of the object, and calculate a relative position of the objectbetween the first pattern and the second pattern imaged by the sensor.

In another aspect of this disclosure, an image forming apparatusincludes a detector to detect an object, and a head to form an image onthe object according to a detection of the detector. The detectorincludes a light source to irradiate an object with light, a sensor toimage a first pattern and a second pattern formed on the object with thelight irradiated by the light source, the first pattern and the secondpattern imaged by the sensor at different times, and a circuit to:control the light source to adjust a light quantity of the lightaccording to a type of the object and irradiate the object with thelight quantity adjusted according to the type of the object, calculate arelative position of the object between the first pattern and the secondpattern imaged by the sensor, and control the head to form the image onthe object according to the relative position.

In still another aspect of this disclosure, a reading apparatus includesa detector to detect an object, and a reading head to read an image onthe object according to a detection of the detector. The detectorincludes a light source to irradiate an object with light, a sensor toimage a first pattern and a second pattern formed on the object with thelight irradiated by the light source, the first pattern and the secondpattern imaged by the sensor at different times, and a circuit to:control the light source to adjust a light quantity of the lightaccording to a type of the object and irradiate the object with thelight quantity adjusted according to the type of the object, calculate arelative position of the object between the first pattern and the secondpattern imaged by the sensor, and control the head to read the image onthe object according to the relative position.

In still another aspect of this disclosure, an adjustment methodincludes irradiating an object with light, imaging a first pattern and asecond pattern formed on the object with the light irradiated to theobject, the first pattern and the second pattern imaged by the sensor atdifferent times, adjusting a light quantity according to a type of theobject, irradiating the object with the light quantity of the lightadjusted according to the type of the object, and calculating a relativeposition of the object between the first pattern and the second pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned and other aspects, features, and advantages of thepresent disclosure will be better understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawings, wherein:

FIG. 1 is a schematic perspective view of an image forming apparatusaccording to a first embodiment of the present disclosure;

FIG. 2 is a schematic cross-sectional view of the image formingapparatus according to the first embodiment of the present disclosure;

FIG. 3 is a schematic plan of the image forming apparatus according tothe first embodiment of the present disclosure;

FIGS. 4A and 4B are schematic views illustrating external shapes of thehead unit according to the present disclosure;

FIG. 5 is a schematic block diagram illustrating a hardwareconfiguration of a detector according to a first embodiment of thepresent disclosure;

FIG. 6 is an external perspective view of a sensor device according tothe present disclosure;

FIG. 7 is a schematic block diagram of a functional configuration of thedetector according to the present disclosure;

FIG. 8 is a block diagram of a calculator according to the presentdisclosure;

FIG. 9 is a graph illustrating a peak position according to the presentdisclosure;

FIG. 10 is a graph illustrating a result of correlation operationaccording to the present disclosure;

FIG. 11 is a schematic block diagram of a controller according to thepresent disclosure;

FIG. 12 is a block diagram of a configuration of a data managementdevice;

FIG. 13 is a block diagram of a hardware configuration of an imageoutput device of the controller;

FIG. 14 is a timing chart of detecting the position of the web performedby the image forming apparatus according to the present disclosure;

FIG. 15 is a timing chart of a process timing of the image formingapparatus according to the present disclosure;

FIG. 16 is a flowchart of a process of adjustment of a light quantity bythe detection device according to the present disclosure;

FIG. 17 is a schematic cross-sectional view of an image formingapparatus according to a comparative example;

FIG. 18 is a graph illustrating an example of displacement in an inkdischarge position when the ink lands on the web in a state withoutadjustment;

FIG. 19 is a graph illustrating an influence of the roller eccentricityon displacement in ink discharge position;

FIG. 20 is a graph illustrating an example of an experimental result foreach object according to a present disclosure;

FIG. 21 is a graph illustrating an example of an experimental resultwhen the object is a plain paper according to a present disclosure;

FIG. 22 is a graph illustrating an example of an experimental resultwhen the object is a coated paper according to a present disclosure;

FIG. 23 is a graph illustrating a result of an adjustment by thedetector according to the present disclosure;

FIG. 24 is a graph illustrating a result of an adjustment by thedetector according to the present disclosure;

FIG. 25 is a schematic view of a variation of a liquid dischargeapparatus according to the present disclosure;

FIG. 26 is a schematic cross-sectional view of the image formingapparatus according to a second embodiment of the present disclosure;

FIG. 27 is a schematic plan view of a reading apparatus according to athird embodiment of the present disclosure;

FIG. 28 is a schematic cross-sectional view of the reading apparatusaccording to another embodiment of the present disclosure;

FIG. 29 is a schematic plan view of a process position of the head unitsHD1 and HD2 according to the present disclosure;

FIG. 30 is a schematic block diagram of a functional configuration ofthe reading apparatus according to the present disclosure; and

FIGS. 31A and 31B are schematic perspective views of the detectiondevice according to another embodiment of the present disclosure.

The accompanying drawings are intended to depict embodiments of thepresent disclosure and should not be interpreted to limit the scopethereof. The accompanying drawings are not to be considered as drawn toscale unless explicitly noted.

DETAILED DESCRIPTION

In describing embodiments illustrated in the drawings, specificterminology is employed for the sake of clarity. However, the disclosureof this patent specification is not intended to be limited to thespecific terminology so selected and it is to be understood that eachspecific element includes all technical equivalents that have the samefunction, operate in an analogous manner, and achieve similar results.

Although the embodiments are described with technical limitations withreference to the attached drawings, such description is not intended tolimit the scope of the disclosure and all the components or elementsdescribed in the embodiments of this disclosure are not necessarilyindispensable. As used herein, the singular forms “a”, “an”, and “the”are intended to include the plural forms as well, unless the contextclearly indicates otherwise.

Hereinafter, embodiments of the present disclosure are described withreference to the attached drawings.

An embodiment is described below with reference to the drawings. For thefollowing embodiments, components having the same function andconfiguration are appended with the same reference codes and redundantdescription thereof may be omitted.

A process apparatus including a detector is described below as anexample. In this example, the process apparatus performs a process on anobject with a head unit. As an example of the process apparatus, thereis a liquid discharge apparatus that performs a process of discharging aliquid onto a web by the head unit.

The web is an example of an object on which an image is formed. Theimage is formed on the web when a liquid is discharged onto the web fromthe head unit. Hereinafter, an example of the liquid dischargingapparatus is described below as an image forming apparatus that formsimage on the object such as the web.

Further, a “liquid discharge head unit” that discharges liquid isdescribed as an example of the “head unit”, and the position in the webwhere the liquid lands is an example of “process position”. Hereinafter,the “liquid discharge head unit” is simply referred to as the “headunit”.

General Configuration

FIG. 1 is a schematic perspective view of an image forming apparatusaccording to a first embodiment of the present disclosure. In such animage forming apparatus, the liquid to be discharged is a recordingliquid such as aqueous ink or oil-based ink. The image forming apparatus110 includes a conveyor to convey an object such as a web 120.

Examples of the “object” include a recording medium. The web 120 is anexample of the recording medium. In the illustrated example, the imageforming apparatus 110 includes a roller 130 and the like to convey theweb 120 and discharges liquid onto the web 120 to form an image on theweb 120. The web 120 is a so-called continuous sheet. That is, the web120 is, for example, paper in the form of roll that can be wound arounda roller.

The image forming apparatus 110 is a so-called production printer. Inthe following description, the roller 130 adjusts a tension of the web120 and conveys the web 120 in a conveyance direction 10 as indicated byarrow in FIG. 1. Further, in the following description, a directionperpendicular to the conveyance direction 10 is referred to as anorthogonal direction 20. In this example, the image forming apparatus110 is an inkjet printer to discharge four color inks, namely, black(K), cyan (C), magenta (M), and yellow (Y) inks, to form an image on apredetermined position of the web 120.

FIG. 2 is a schematic cross-sectional view illustrating a generalstructure of the image forming apparatus 110 according to a firstembodiment of the present disclosure. As illustrated in FIG. 2, theimage forming apparatus 110 includes four liquid discharge head units210 (210Y, 210M, 210C, and 210K) to discharge four colors of inks,respectively. Hereinafter, the “liquid discharge head unit” is simplyreferred to as “head unit”.

Each of the head units 210 discharges a corresponding color of ink ontothe web 120 conveyed in the conveyance direction 10. The image formingapparatus 110 includes two pairs of nip rollers NR1 and NR2, a roller230, and the like, to convey the web 120. One of the two pairs of niprollers are a first nip roller pair NR1 disposed upstream from the headunits 210 in the conveyance direction 10.

The other of the two pairs of nip rollers is a second nip roller pairNR2 disposed downstream from the first nip roller pair NR1 and the headunits 210 in the conveyance direction 10. Each of the nip roller pairsNR1 and NR2 rotates while nipping the object, such as the web 120, asillustrated in FIG. 2. The nip roller pairs NR1 and NR2 and the roller230 together serve as a mechanism to convey the object (e.g., the web120) in the conveyance direction.

The recording medium such as the web 120 is preferably a long sheet.Specifically, the web 120 is preferably longer than a distance betweenthe first nip roller pair NR1 and the second nip roller pair NR2. Therecording medium is not limited to the web 120. For example, therecording medium may be a folded sheet (so-called fanfold paper orZ-fold paper).

In the general structure illustrated in FIG. 2, the head units 210 arearranged in the order of black (K), cyan (C), magenta (M), and yellow(Y) from upstream to downstream in the conveyance direction 10.Specifically, a head unit 210K for black (K) is disposed on the mostupstream in the conveyance direction 10. A head unit 210C for cyan (C)is disposed next to and downstream from the head unit 210K. Further, ahead unit 210M for magenta (M) is disposed next to and downstream fromthe head unit 210C for cyan (C). Further, a head unit 210Y for yellow(Y) is disposed on the most downstream in the conveyance direction 10.

Each of the head units 210 discharges a corresponding color of ink to apredetermined position on the web 120 according to the image data, forexample. A position at which the head unit 210 discharges ink(hereinafter “ink discharge position”) is almost identical to a positionat which ink droplets discharged from the liquid discharge head unit 210strike the surface of the recording medium (hereinafter “ink dischargeposition”). In other words, the ink landing position may be directlybelow the ink discharge position of the head unit 210. Thus, “inkdischarge position” is almost identical to the “ink landing position”,and the “ink discharge position” on the web 120 can be changed bycontrolling the “ink discharge position” of the head unit 210.

In the present embodiment, black ink is discharged onto the inkdischarge position of the head unit 210K (hereinafter “black inkdischarge position PK”). Similarly, cyan ink is discharged onto the inkdischarge position of the head unit 210C (hereinafter “cyan inkdischarge position PC”). Magenta ink is discharged onto the inkdischarge position of the head unit 210M (hereinafter “magenta inkdischarge position PM”). Yellow ink is discharged onto the ink dischargeposition of the head unit 210Y (hereinafter “yellow ink dischargeposition PY”).

The controller 520 controls a process timing at which each head unit 210discharges ink. The controller 520 also controls actuators AC1, AC2,AC3, and AC4 provided for each head unit 210. The controller 520 isconnected to each head unit 210. Both of the control of the processtiming and the actuators AC1, AC2, AC3, and AC4 may be performed by twoor more controllers or circuits, instead of being performed by thecontroller 520. A detail of the actuators is described below.

In FIG. 2, each head unit 210 is provided with a plurality of rollers.For example, in FIG. 2, the image forming apparatus 110 includes theplurality of rollers respectively disposed upstream and downstream fromeach head unit 210. Thus, the head units 210 are disposed between theplurality of rollers in the conveyance direction 10.

Specifically, a first roller CR1K to convey the web 120 to the black inkdischarge position PK is disposed upstream from the head unit 210K forblack. Similarly, the roller disposed downstream from the head unit 210Kis referred to as a second roller CR2K to convey the web 120 from theink discharge position PK. Disposing the first roller CR1 and the secondroller CR2 for each ink discharge position PK, PC, PM, and PY cansuppress fluttering of the recording medium conveyed at each inkdischarge position. Here, the first roller CR1 and the second roller CR2used to convey the web 120 (recording medium) are driven rollers.Alternatively, the first roller CR1 and the second roller CR2 may bedriven by a motor or the like.

Note that the first roller CR1 as an example of the first support andthe second roller CR2 as an example of the second support do not have tobe a rotating body such as a driven roller. Thus, the first support andthe second support may be members that support the object (web 120). Forexample, each of the first and second supports may be a pipe or a shafthaving a round (circular) cross section. Alternatively, each of thefirst and second supports may be a curved plate having a curved face tocontact the object (web 120). In the following description, the firstsupport is the first roller CR1, and the second support is the secondroller CR2.

Specifically, a first roller CR1K for black to convey the web 120 to theblack ink discharge position PK is disposed upstream from the head unit210K in the conveyance direction 10. A second roller CR2K for blackconveys the web 120 from the black ink discharge position PK to thedownstream side in the conveyance direction 10.

Similarly, a first roller CR1C and a second roller CR2C for cyan aredisposed upstream and downstream from the head unit 210C for cyan,respectively, in the conveyance direction 10. Similarly, a first rollerCR1M and a second roller CR2M for magenta are disposed upstream anddownstream from the head unit 210M, respectively, in the conveyancedirection 10. Similarly, a first roller CR1Y and a second roller CR2Yfor yellow are disposed upstream and downstream from the head unit 210Y,respectively, in the conveyance direction 10.

The image forming apparatus 110 includes, for example, at least onesensor device (e.g., sensor devices SENK, SENC, SENM, and SENY, alsocollectively “sensor device SEN”) for the head units, respectively, asillustrated in FIG. 2. The sensor device SEN detects a position of theweb 120 in the conveyance direction 10, the orthogonal direction 20, orboth of the conveyance direction 10 and the orthogonal direction 20. Thesensor device SEN includes an optical sensor OS that utilizes light suchas visible light or infrared light, for example.

For example, the optical sensor OS is a charge-coupled device (CCD)camera or a complementary metal oxide semiconductor (CMOS) camera. Thesensor device SEN may not include the optical sensor OS, but preferablyincludes a two-dimensional sensor. The sensor device SEN, for example,detects the surface of the web 120. Further, the sensor device SEN iscapable of detecting a back surface or a front surface of the web 120 asthe object (recording medium) during image formation as described below.

Further, the sensor device SEN includes a laser light source that emitslaser light as described below. As the laser light emitted from alight-emitting element is diffused on the surface of the web 120 andsuperimposed diffusion waves interfere with each other, a pattern suchas a speckle pattern appears. The optical sensor OS of each of thesensor devices SEN captures and images the speckle pattern, for example,to generate image data. Based on a position change of the specklepattern captured by the optical sensor OS, the image forming apparatus110 can obtain a moving amount of each of the head units 210 to move thehead units 210 and discharge timing of each of the head units 210, forexample.

Hereinafter, the term “sensor position” means a position where adetection of the position of the web 120, etc., is performed by thesensor devices SEN. Accordingly, it is not necessary that all componentsrelating to the detection are disposed at the “sensor position”. Thatis, the hardware constituting a detector may be installed at a positionwhere the detection is performed. On the other hand, only the opticalsensor OS may be installed at a position where detection is performed asa sensor, and the other devices may be connected to the optical sensorOS with a cable and placed at another position. Further, in thefollowing description, each sensor such as the optical sensor OS issometimes simply referred to as “sensor” as a whole.

The sensor device SEN is preferably disposed closer to the ink dischargeposition of the head unit 210. The sensor is installed for each of thehead units 210.

Specifically, in the example as illustrated in FIG. 2, the sensor deviceSENK for black is preferably disposed in an inter-roller range INTK1 forblack between the first and second rollers CR1K and CR2K for black. InFIG. 2, the inter-roller range INTK1 for black is disposed between thefirst and second rollers CR1K and CR2K for black.

Similarly, the sensor device SENC for cyan is preferably disposed in aninter-roller range INTC1 for cyan between the first and second rollersCR1C and CR2C. In FIG. 2, the inter-roller range INTC1 for cyan isdisposed between the first and second rollers CR1C and CR2C for cyan.

The sensor device SENM for magenta is preferably disposed in aninter-roller range INTM1 between the first and second rollers CR1M andCR2M. In FIG. 2, the inter-roller range INTM1 for magenta is disposedbetween the first and second rollers CR1M and CR2M for magenta.

The sensor device SENY for yellow is preferably disposed in aninter-roller range INTY1 between the first and second rollers CR1Y andCR2Y for yellow. In FIG. 2, the inter-roller range INTY1 for yellow isdisposed between the first and second rollers CR1Y and CR2Y for yellow.

The “sensor positions” are preferably between the first and secondrollers CR1 and CR2 and at positions close to the first rollers CR1 fromthe ink discharge positions PK, PC, PM, and PY, respectively. In otherwords, the “sensor position” is preferably upstream from ink dischargeposition in the conveyance direction 10.

Specifically, the sensor device SENK for black is, more preferably,disposed in a range extending from the black ink discharge position PKupstream to the first roller CR1K for black in the conveyance direction10 (hereinafter “upstream range INTK2”).

Similarly, the sensor device SENC for cyan is, more preferably, disposedin a range extending from the cyan ink discharge position PC upstream tothe first roller CR1C for cyan (hereinafter “upstream range INTC2”).

The sensor device SENM for magenta is, more preferably, disposed in arange extending from the magenta ink discharge position PM upstream tothe first roller CR1M for magenta (hereinafter “upstream range INTM2”).

The sensor device SENY for yellow is, more preferably, disposed in arange extending from the yellow ink discharge position PY upstream tothe first roller CR1Y for yellow (hereinafter “upstream range INTY2”).

When the sensor devices SEN are respectively disposed in the upstreamranges INTK2 for black, INTC2 for cyan, INTM2 for magenta, and INTY2 foryellow, the image forming apparatus 110 can detect the position or thelike of the web 120 (object) with a high accuracy. The sensor devicesSENK, SENC, SENM, and SENY are thus disposed upstream from the inkdischarge position (ink landing position) PK, PC, PM, and PY,respectively, in the conveyance direction 10. Therefore, the imageforming apparatus 110 detects the positions or the like of the web 120in the conveyance direction 10, the orthogonal direction 20, or both, ata position upstream from the ink discharge positions PK, PC, PM, and PYby the sensor devices SENK, SENC, SENM, and SENY, respectively.

Thus, the image forming apparatus 110 can calculate respective inkdischarge timings (i.e., process timing) of the head units 210, theamount by which the head unit 210 is to move (i.e., head moving amount),or both. That is, after the position or the like of the web 120 isdetected upstream from the ink discharge positions PK, PC, PM, and PY,the web 120 is conveyed to the ink discharge positions PK, PC, PM, andPY.

While the web 120 is conveyed to the ink discharge positions PK, PC, PM,and PY, the image forming apparatus 110 can calculate the process timingor move the head unit 210 to change the ink discharge positions PK, PC,PM, and PY (process position). Thus, the image forming apparatus 110 canchange the process position (ink discharge position) with a highaccuracy.

On the other hand, if the “sensor positions” where the sensor isinstalled is directly below each head unit 210, the process position(ink discharge position, or ink landing position) may be shifted due toa delay in control operation or the like. Accordingly, the “sensorpositions (sensor devices SENK, SENC, SENM, SENY)” are disposed upstreamfrom the ink discharge positions PK, PC, PM, and PY, respectively. Thus,the image forming apparatus 110 can reduce shifting of the processposition (ink discharge position) and control the process position (inkdischarge position) with a high accuracy.

There is a case in which it is difficult to dispose the sensor devicesSEN adjacent to the ink discharge positions PK, PC, PM, and PY. However,if the delay in the control operation is ignored, the “sensor positions”may be directly under each of the head units 210 or the like. If thesensor devices SEN are disposed directly below the head units 210,respectively, the sensor devices SEN can detect an accurate movingamount of the web 120 directly below the head unit 210. Therefore, in aconfiguration capable of performing the control operation at a fasterspeed, the sensor devices SEN are preferably disposed closer to theposition directly below each head units 210.

Alternatively, in a configuration in which an error is tolerable, thesensor position (sensor devices SEN) may be disposed directly below thehead unit 210, or downstream from a position directly below the headunit 210 in the inter-roller range INT1 between the first roller CR1 andthe second roller CR2.

As illustrated in FIG. 2, the image forming apparatus 110 preferablyincludes at least one sensor SEN2 disposed upstream from the sensordevices SEN of each of the head units 210. Specifically, the imageforming apparatus 110 preferably includes a second sensor device SEN2 inaddition to sensor devices SEN installed for each of the head units 210.Hereinafter, as illustrated in FIG. 2, an example of installing thesecond sensor device SEN2 in the image forming apparatus 110 isdescribed below.

FIG. 3 is a schematic plan view illustrating a configuration of theimage forming apparatus 110 according to a first embodiment of thepresent disclosure.

Referring to FIG. 3, when viewed in a direction vertical to a recordingsurface of the web 120, for example, each of the sensor devices SEN ispreferably disposed at a position close to an end of the web 120 in awidth direction (the orthogonal direction 20) of the web 120 andoverlapping with the web 120. Each of the sensor devices SEN is arrangedat the positions PS20, PS1, PS2, PS3, and PS4, respectively. In theconfiguration illustrated in FIGS. 2 and 3, the controller 520 cancontrol actuators AC1, AC2, AC3, and AC4 to move the head units 210K,210C, 210M, and 210Y, respectively, in the orthogonal direction 20perpendicular to the conveyance direction 10 of the web 120.

As illustrated in FIGS. 2 and 3, the sensor devices SEN are disposedfacing a back side of the web 120 opposite the head units 210. That is,the sensor devices SEN are disposed opposite to positions where each ofthe head units 210 are installed with respect to the web 120.

The image forming apparatus 110 includes actuator controllers CTL1,CTL2, CTL3, and CTL4 connected to the actuators AC1, AC2, AC3, and AC4,respectively to control the actuators AC1, AC2, AC3, and AC4.Hereinafter, the actuators AC1, AC2, AC3 and AC4 are collectivelyreferred to as “actuator AC”. Hereinafter, the actuator controllersCTL1, CTL2, CTL3 and CTL4 are collectively referred to as “actuatorcontroller CTL”.

The actuator AC is, for example, a linear actuator or a motor. Further,the actuator AC may include a control circuit, a power supply circuit,mechanical parts, and the like.

The actuator controllers CTL1, CTL2, CTL3 and CTL4 are, for example,driver circuits and the like.

FIGS. 4A and 4B are schematic views illustrating external shapes of thehead unit 210 according to the present disclosure. FIG. 4A is aschematic plan view of one of the four head units 210K to 210Y of theimage forming apparatus 110. FIG. 4B is a schematic plan view of one ofa liquid discharge head 210K-1 for black in the head unit 210K for blackaccording to the present disclosure. Hereinafter, the “liquid dischargehead” is simply referred to as “head”.

As illustrated in FIG. 4A, the head units 210 (210K, 210C, 210M, and210Y) according to the present embodiment are a line-type head unit.

The head unit 210K includes four heads 201K-1, 210K-2, 210K-3, and210K-4 for black arranged in a staggered manner in the orthogonaldirection 20 perpendicular to the conveyance direction 10. The head210K-1 has a shape as illustrated in FIG. 4B. With this arrangement, thehead unit 210K for black can form an image throughout the imageformation area (so-called printing area) on the web 120 in the widthdirection (orthogonal direction 20) perpendicular to the conveyancedirection 10 with black ink. Each of the other head units 210C, 210M,and 210Y has a similar structure with the head unit 210K, and thus thedescriptions of which is omitted.

Although an example of the head units 210 each including four heads isdescribed above, alternatively, the head unit 210 may include a singlehead.

[Example of Detector]

FIG. 5 is a schematic block diagram illustrating a hardwareconfiguration of a detector 600 according to a first embodiment of thepresent disclosure. For example, the detector 600 includes a hardwaresuch as the sensor device SEN and a controller 520 as illustrated inFIG. 5. The sensor device SEN includes a light source LG, an opticalsensor OS, a control circuit 52, and a memory device 53.

A specific structure of the sensor device SEN is described below.

FIG. 6 is an external perspective view of the sensor device SENaccording to the present embodiment. The sensor device SEN illustratedin FIG. 6 is configured to capture and image a pattern such as thespeckle pattern described above. The speckle pattern appears on asurface of the web 120 (object) when the web 120 is irradiated with alight from the light source LG. Specifically, the sensor device SEN hasa laser light source as an example of the light source LG.

The sensor device SEN includes an optical system such as collimateoptical system using a collimator lens (CL). The sensor device SENfurther includes a CMOS image sensor and a telecentric optical system TOto capture and image the pattern such as the speckle pattern. The CMOSimage sensor serves as the optical sensor OS. The telecentric opticalsystem TO condenses light to form an image of the speckle pattern on theCMOS image sensor (optical sensor OS).

For example, the optical sensor OS captures and images the pattern suchas the speckle pattern. The controller 520 in FIG. 5 performs processingsuch as cross-correlation calculation based on a pattern imaged by oneoptical sensor OS of one sensor device SEN and a pattern imaged byanother optical sensor OS of another sensor device SEN to obtain aposition of a correlation peak.

Next, the controller 520 outputs an amount of movement of the web 120(object) moved from the one optical sensor OS to another optical sensorOS based on an amount of displacement of the position of the correlationpeak calculated by the correlation operation. In the example illustratedin FIG. 6, the sensor device SEN is 15 mm in width as indicated by arrowW, 60 mm in depth indicated by arrow D, and 32 mm in height indicated byarrow H (15×60×32). A detail of the correlation operation is describedbelow.

The CMOS image sensor is an example of hardware that implements imagingunits 16A and 16B illustrated in FIG. 7. In this example, the hardwarefor performing the correlation calculation is described as thecontroller 520. However, the correlation calculation may be executed byan FPGA circuit mounted on any one of the sensor devices SEN.

The control circuit 52 controls the optical sensor OS, the laser lightsource LG, and the like inside the sensor device SEN. Specifically, thecontrol circuit 52 outputs trigger signals to the optical sensor OS tocontrol shutter timing of the optical sensor OS, for example. Thecontrol circuit 52 causes the optical sensor OS to generatetwo-dimensional image data and acquires the two-dimensional images fromthe optical sensor OS.

Then, the control circuit 52 transmits the two-dimensional image datagenerated by the optical sensor OS to the memory device 53 or the like.Further, the control circuit 52 outputs a signal for controlling thelight quantity to the laser light source 51 or the like. The controlcircuit 52 may be implemented by a FPGA circuit, for example.

The memory device 53 is a so-called memory, for example. The memorydevice 53 preferably has a configuration to divide the two-dimensionalimage data transmitted from the control circuit 52 and to store indifferent storage areas.

The controller 520 performs calculation using image data stored in thememory device 53 and the like. Further, the controller 520 includes amemory 521 to store a type of the object (web 120) adjusted in the pastand an amount of light associated with the type of the object.

The control circuit 52 and the controller 520 are, for example, acentral processing unit (CPU) or electronic circuits. Note that thecontrol circuit 52, the memory device 53, and the controller 520 are notnecessarily discrete devices. For example, the control circuit 52 andthe controller 520 may be implemented by a single CPU.

FIG. 7 is a schematic block diagram of a functional configuration of thedetector 600 according to the present disclosure. As illustrated in FIG.7, the detector 600 detects the position of the web 120 and the likeusing a combination of the sensor device SENK installed for the headunit 210K for black and the sensor device SENC installed for the headunit 210C for cyan among the sensor devices SEN installed for each ofthe head units 210.

As illustrated in FIG. 7, the sensor device SENK for the head unit 210Kfor black includes an image acquiring unit 52A which functions as animage obtainer. The image acquiring unit 52A outputs image data imaged(captured) at “position A”. The sensor device SENC for the head unit210C for cyan includes an image acquiring unit 52B which functions as animage obtainer. The image acquiring unit 52B outputs image data imaged(captured) at “position B”.

First, the image acquiring unit 52A for the head unit 210K for blackincludes, for example, an imaging unit 16A, an imaging controller 14A,an image storing unit 15A, light source unit 51A, and a light sourcecontroller 56A, for example. In this example, the image acquiring unit52B for the head unit 210C for cyan has a similar configuration with theimage acquiring unit 52A for the head unit 210K. Thus, the imageacquiring unit 52B for the head unit 210C includes an imaging unit 16B,an imaging controller 14B, an image storing unit 15B, a light sourceunit 51B, a light source controller 56B, for example. In the following,the image acquiring unit 52A is described below as an example.

As illustrated in FIG. 7, the imaging unit 16A captures and images animage of the web 120 conveyed in the conveyance direction 10. Theimaging unit 16A is implemented by, for example, the optical sensor OSas illustrated in FIG. 5, for example.

The imaging controller 14A includes a shutter controller 141A and animage acquisition unit 142A. The imaging controller 14A is implementedby, for example, the control circuit 52 as illustrated in FIG. 5, forexample.

The image acquisition unit 142A acquires image data captured and imagedby the imaging unit 16A.

The shutter controller 141A controls the imaging unit 16A to controltiming of capturing and imaging the web 120.

The image storing unit 15A stores the image data acquired by the imagingcontroller 14A. The image storing unit 15A is implemented by, forexample, the memory device 53 illustrated in FIG. 5, for example.

The light source unit 51A irradiates light such as laser light to theweb 120. The light source unit 51A is implemented by, for example, thelight source LG as illustrated in FIG. 5, for example.

The light source controller 56A controls turning ON or turning OFF ofthe light source unit 51A and the amount of light irradiated from thelight source unit 51A, for example. The light source controller 56A isimplemented by, for example, the control circuit 52 as illustrated inFIG. 5, for example.

A calculator 53F calculates the position of the pattern on the web 120,a speed at which the web 120 moves (hereinafter “moving speed”), and anamount of movement of the web 120 (hereinafter “moving amount”) based onthe image data respectively stored in the image storing unit 15A and15B.

Further, the calculator 53F outputs data on time difference Δtindicating the timing of shooting (shutter timing) the web 120 to theshutter controller 141A. Thus, the calculator 53F may instruct theshutter controller 141A and the shutter controller 141B to control theshutter timings to capture and image the image data indicating theposition A and the image data indicating the position B, respectively,with the time difference Δt. The calculator 53F is implemented by, forexample, the controller 520 as illustrated in FIG. 5, for example.

The web 120 has diffusiveness on a surface of the web 120 or in aninterior of the web 120. Accordingly, when the web 120 is irradiatedwith the laser light from the light source unit 51A and the light sourceunit 51B, the reflected light is diffused. The diffuse reflectioncreates a pattern on the web 120. The pattern is made of spots called“speckle” (i.e., a speckle pattern). Thus, when the web 120 is imaged bythe imaging unit 16A, an image data indicating the speckle pattern isobtained.

The detector 600 includes an adjusting unit 55F to control the lightsource controller 56A. Particularly, the amount of light received by theimaging unit 16A and 16B is different according to types of the object(web 120). For example, even when an identical amount of the laser lightis irradiated to the object (web 120), the amount of the laser lightreflected on a surface of a normal paper and a coated paper isdifferent.

Therefore, the adjusting unit 55F controls the light source controller56A and adjusts the light quantity of the light irradiated from each ofthe light source unit 51A and the light source unit 51B based on theimage data captured and imaged by each imaging unit 16A and 16B. Thecalculator 53F and the adjusting unit 55F are implemented by, forexample, the controller 520 as illustrated in FIG. 5, for example.

As described above, the detector 600 can detect the position of thespeckle pattern on the web 120 from the image data, and the detector 600can detect the position of the web 120. The speckle pattern is appearedby the laser light irradiated to the web 120. The laser light interferesby an uneven shape on the surface or interior of the web 120.

As the web 120 is conveyed, the speckle pattern on the web 120 isconveyed (moved) as well. Thus, when an identical speckle pattern on theweb 120 is detected at different time points at the position A and theposition B by the image acquiring units 52A and 52B, respectively, thecalculator 53F of the image forming apparatus 110 can calculate themoving amount of the web 120 based on an amount of movement(hereinafter, “moving amount”) of the identical speckle pattern on theweb 120. In other words, the calculator 53F calculates the moving amountof the speckle pattern based on the detection of an identical specklepattern at the position A (upstream side) and the position B (downstreamside) by the image acquiring units 52A and 52B, respectively.

Thus, the calculator 53F can calculate the moving amount of the web 120from the moving amount of the speckle pattern. Further, the calculator53F converts the calculated moving amount into a moving amount per unittime. Thus, the calculator 53F can calculate the moving speed of the web120.

As illustrated in FIG. 7, the imaging unit 16A and the imaging unit 16Bis spaced apart with a predetermined interval in the conveyancedirection 10. The imaging units 16A and 16B image (capture) images ofthe web 120 at the positions A and the position B, respectively. Thus, afirst pattern imaged by the imaging unit 16A and the second patternimaged by the imaging unit 16B are imaged at different position.

The shutter controllers 141A and 141B control the imaging units 16A and16B to image the web 120 at an interval of time difference Δt.Specifically, based on the pattern represented by the image datagenerated by the imaging, the calculator 53F obtains the amount ofmovement of the web 120. The time difference Δt can be expressed byFormula 1 below, where V represents a conveyance speed (mm/s) in anideal condition without displacement, and L represents a relativedistance, which is the distance (mm) between the imaging unit 16A andthe imaging unit 16B in the conveyance direction 10.

Δt=L/V:  Formula 1

In Formula 1, a relative distance L is an interval between the sensordevice SENK and the sensor device SENC. Thus, the relative distance canbe determined by measuring the interval between the sensor device SENKand the sensor device SENC in advance.

Further, the calculator 53F performs a cross-correlation operation ofimage data “D1(n)” imaged by the image acquiring unit 52A and image data“D2(n)” imaged by the image acquiring unit 52B. Hereinafter, image datagenerated by the cross-correlation operation is referred to as“correlated image”. For example, the calculator 53F calculates adisplacement amount ΔD(n) based on the correlated image. Thedisplacement amount ΔD(n) is an amount of displacement of the web 120.

For example, the cross-correlation operation is expressed by Formula 2below.

D1*D2*=F−1[F[D1]·F[D2]*]  Formula 2

In Formula 2, “D1” represents image data “D1(n)” of the image imaged atthe position A by the image acquiring unit 52A. Similarly, in Formula 2,“D2” represents image data “D2(n)” of the image imaged at the position Bby the image acquiring unit 52B. In Formula 2, “F[ ]” represents Fouriertransform, and “F−1[ ]” represents inverse Fourier transform. Further,“*” represents complex conjugate, and “*” represents cross-correlationoperation in above Formula 2.

As indicated in the Formula 2, when cross-correlation operation “D1*D2”is performed on the image data D1 and D2, image data indicating thecorrelation image is obtained. When the image data D1 and D2 aretwo-dimensional image data, the image data representing the correlationimage becomes two-dimensional image data. When the image data D1 and D2are one-dimensional image data, the image data representing thecorrelation image becomes one-dimensional image data.

When a broad luminance distribution causes an error in the correlationimage, phase only correlation may be used. For example, phase onlycorrelation is expressed by Formula 3 below.

D1*D2*=F−1[P[F[D1]]·P[F[D2]*]]:  Formula 3

In Formula 3, “P[ ]” represents taking only phase out of complexamplitude. Note that the amplitude is considered to be “1”.

Thus, the calculator 53F can calculate the displacement amount ΔD(n)based on the correlation image even when the luminance distribution isrelatively broad.

The correlation image indicates a correlation between the image data D1and the image data D2. Specifically, as the match rate between the imagedata D1 and the image data D2 increases, a luminance indicating a sharppeak (so-called correlation peak) is output at a position close to acenter of the correlation image. When the image data D1 matches theimage data D2, the center of the correlation image and the position ofthe peak of the image data D1 match the center of the correlation imageand the position of the peak of the image data D2.

The calculator 53F outputs information such as a difference in thepositions between the image data D1 and D2 at the time difference Δt,the moving amount of the web 120, and the moving speed of the web, forexample, based on the result of the correlation calculation. Forexample, the detector 600 can detect the moving amount of the web 120 inthe orthogonal direction 20 between the image data D1 and the image dataD2. The detector 600 may detect the moving speed instead of the movingamount. The calculator 53F can calculate the moving amount of the headunit 210C for cyan from the result of the correlation calculation.

The head moving unit 57F controls the actuator AC2 in FIGS. 3 and 7 tocontrol the ink discharge position of the liquid based on a calculationresult of the calculator 53F. The head moving unit 57F is constitutedby, for example, an actuator controller CTL (CTL1 through CTL4 in FIG.3). The function of the head moving unit 57F may be configured not onlyby the actuator controller CTL but also by the combination of theactuator controller CTL and the controller 520 in FIG. 5. Further, thefunction of the head moving unit 57F may be configured by the controller520.

Further, the calculator 53F may also calculate a difference between themoving amount of the web 120 and a relative distance L in the conveyancedirection 10. As illustrated in FIG. 7, the relative distance L is adistance between the imaging units 16A and 16B. Further, the calculator53F may also calculate and detect the position of the web 120 in theconveyance direction 10 and the orthogonal direction 20 from thetwo-dimensional image data imaged by the imaging units 16A and 16B.Thus, the calculator 53F can reduce a cost of detecting the position ofthe web 120 in both directions of the conveyance direction 10 and theorthogonal direction 20. The present embodiment can also reduce numbersof the sensors and thus reduce a space for the detection.

The calculator 53F calculates a discharge timing of the head unit 210Cfor cyan based on the calculation of difference between the movementamount of the web 120 from an ideal distance (relative distance L).Based on this calculation result of the discharge timing by thecalculator 53F, the discharge controller 54F controls the head unit 210Cfor cyan to discharge cyan ink from the head unit 210C.

The discharge controller 54F outputs a second signal SIG2 to control thedischarge timing of the head unit 210C for cyan. When the dischargetiming of the head unit 210K is calculated by the calculator 53F, thedischarge controller 54F outputs a first signal SIG1 to the head unit210K for black to control the discharge timing of the head unit 210K.The discharge controller 54F is implemented by, for example, thecontroller 520 as illustrated in FIG. 2 and the like.

The correlation calculation may be calculated as follows, for example.

FIG. 8 is a block diagram of the calculator for executing a correlationcalculation according to the present disclosure. For example, with aconfiguration as illustrated in FIG. 8, the calculator 53F can performthe correlation operation and calculate a relative position, the movingamount, the moving speed, or a combination of above of the web 120 inthe orthogonal direction 20 at the positions A and B in which two ormore image data are imaged by the imaging units 16A and 16B. Thecalculator 53F can also calculate the displacement amount ΔD(n) from anideal conveyance position, the moving speed, for example, of the web 120at the timing of imaging the two or more image data by the imaging units16A and 16B.

Specifically, the calculator 53F includes a first 2D Fourier transformFT1, a second 2D Fourier transform FT2, a correlation image datagenerator DMK, a peak position search unit SR, an arithmetic unit CAL(or arithmetic logical unit), and a transform-result storing unit MEM.

The first 2D Fourier transform FT1 transforms the first image data D1.The first 2D Fourier transform FT1 includes a Fourier transform unit FT1a for transform in the orthogonal direction 20 and a Fourier transformunit FT1 b for transform in the conveyance direction 10. Hereinafter,the Fourier transform unit FT1 a for transforming in the orthogonaldirection 20 is referred to as the “orthogonal Fourier transform unitFT1 a”. The Fourier transform unit FT1 b for transforming in theconveyance direction 10 is referred to as the “conveyance Fouriertransform unit FT1 b”.

The orthogonal Fourier transform unit FT1 a performs one-dimensionaltransform of the first image data D1 in the orthogonal direction 20.Based on a result of transformation by the orthogonal Fourier transformunit FT1 a, the conveyance Fourier transform unit FT1 b performsone-dimensional transform of the first image data D1 in the conveyancedirection 10. Thus, the orthogonal Fourier transform unit FT1 a and theconveyance Fourier transform unit FT1 b perform one-dimensionaltransform of the first image data D1 in the orthogonal direction 20 andthe conveyance direction 10, respectively. The first 2D Fouriertransform FT1 outputs the result of transformation to the correlationimage data generator DMK.

Similarly, the second 2D Fourier transform FT2 transforms the secondimage data D2. Specifically, the second 2D Fourier transform FT2includes a Fourier transform unit FT2 a for transform in the orthogonaldirection 20, a Fourier transform unit FT2 b for transform in theconveyance direction 10, and a complex conjugate unit FT2 c.Hereinafter, the Fourier transform unit FT2 a for transforming in theorthogonal direction 20 is referred to as the “orthogonal Fouriertransform unit FT2 a”. The Fourier transform unit FT2 b for transformingin the conveyance direction 10 is referred to as the “conveyance Fouriertransform unit FT2 b”.

The orthogonal Fourier transform unit FT2 a performs one-dimensionalFourier transform of the second image data D2 in the orthogonaldirection 20. Based on a result of transformation by the orthogonalFourier transform unit FT2 a, the conveyance Fourier transform unit FT2b performs one-dimensional transform of the second image data D2 in theconveyance direction 10. Thus, the orthogonal Fourier transform unit FT2a and the conveyance Fourier transform unit FT2 b performone-dimensional transform on the second image data D2 in the orthogonaldirection 20 and the conveyance direction 10, respectively.

Next, the complex conjugate unit FT2 c calculates a complex conjugate ofthe results of transformation by the orthogonal Fourier transform unitFT2 a and the conveyance Fourier transform unit FT2 b. Then, the second2D Fourier transform FT2 outputs, to the correlation image datagenerator DMK, the complex conjugate calculated by the complex conjugateunit FT2 c.

The correlation image data generator DMK then generates the correlationimage data based on the result of transformation of the first image dataD1 output from the first 2D Fourier transform FT1 and the result oftransformation of the second image data D2 output from the second 2DFourier transform FT2.

The correlation image data generator DMK includes an adder DMKa and a 2Dinverse Fourier transform unit DMKb.

The adder DMKa adds the result of transformation of the first image dataD1 to the result of transformation of the second image data D2, andoutputs a result of addition to the 2D inverse Fourier transform unitDMKb.

The 2D inverse Fourier transform unit DMKb performs 2D inverse Fouriertransform of the result generated by the adder DMKa. Thus, thecorrelation image data is generated through the 2D inverse Fouriertransform performed by the 2D inverse Fourier transform unit DMKb. Then,the 2D inverse Fourier transform unit DMKb outputs the correlation imagedata to the peak position search unit SR.

The peak position search unit SR searches the correlation image datagenerated by the 2D inverse Fourier transform unit DMKb for a peakposition (a peak of luminance value) at which rising of the luminancevalue is sharpest. First, values indicating the intensity of light, thatis, the degree of luminance, are input to the peak position search unitSR as the correlation image data. Further, the luminance values areinput to the peak position search unit SR in matrix form.

Here, the luminance values are arranged at a pixel pitch of the opticalsensor OS (i.e., an area sensor), that is, pixel size intervals in thecorrelation image data. Thus, the peak position search unit SRpreferably searches for the peak position after performing so-calledsub-pixel processing. The sub-pixel processing enhances an accuracy insearching for the peak position. Thus, the calculator 53F can calculateand output the position, the moving amount, and the moving speed and thelike to the discharge controller 54F.

For example, the peak position searching unit SR search for the peakposition as described below.

FIG. 9 is a graph illustrating the peak position searched in thecorrelation operation according to the present embodiment. In FIG. 9, alateral axis indicates a position of the image in the conveyancedirection 10 in the correlation image data. A vertical axis in FIG. 9indicates the luminance values of each pixel in the correlation imagedata.

The luminance values indicated by the correlation image data aredescribed below using three data of a first data value q1, a second datavalue q2, and a third data value q3. In this example, the peak positionsearch unit SR searches for the peak position P in a curved line kconnecting the first, second, and third data values q1, q2, and q3.

First, the peak position search unit SR calculates difference in theluminance values of each pixel in the correlation image data. Then, thepeak position search unit SR extracts a combination of data values inwhich a value of the difference becomes the largest among the calculateddifferences. Next, the peak position searching unit SR extractscombinations of luminance values adjacent to the combinations of datavalues with the largest difference value. In this way, the peak positionsearching unit SR can extract three data, such as the first data valueq1, the second data value q2, and the third data value q3 as illustratedin FIG. 9.

The peak position search unit SR calculates the curved line k connectingthese three data values q1, q2, and q3 and acquires the peak position P.Thus, the peak position search unit SR can reduce an amount ofoperations such as sub-pixel processing to increase a speed of searchingfor the peak position P. The peak position (a peak of luminance value)at which rising of the luminance value is sharpest is a position of thecombination of data values in which a value of the difference becomesthe largest. The manner of sub-pixel processing is not limited to thedescription above.

Through the searching of the peak position P performed by the peakposition search unit SR, for example, the following result is attained.

FIG. 10 is a graph illustrating a result of correlation operationaccording to the present disclosure. FIG. 10 illustrates a profile ofstrength of correlation of a cross-correlation function. In FIG. 10,each of X-axis and Y-axis indicates serial numbers of pixels. The peakposition search unit SR searches for a peak position such as“correlation peak” in FIG. 10. The strength of correlation illustratedin FIG. 10 indicates the strength of correlation in a condition in whicha red laser light source is used, a light quantity is 60 mW, and aprocess of removing background noise is not performed.

The arithmetic unit CAL calculates the relative position, the movingamount, or the moving speed, or the combination of above of the web 120.For example, the arithmetic unit CAL calculates a difference between acenter position of the correlation image data and the peak positioncalculated by the peak position search unit SR to acquire the relativeposition and the moving amount of the web 120.

Further, the arithmetic unit CAL divides the moving amount of the web120 by time to acquire the moving speed.

Thus, the calculator 53F can calculate the relative position, the movingamount, the moving speed, or the like of the web 120 through thecorrelation operation. The method of calculation of the relativeposition, the moving amount, moving speed, or the like, is not limitedto the method as described above. For example, the calculator 53F mayalternatively acquire the relative position, the moving amount, themoving speed, or the like, through the method as described below.

First, the calculator 53F binarizes each luminance value of the firstimage data D1 and the second image data D2. That is, the calculator 53Fbinarizes the luminance value not greater than a predetermined thresholdvalue into “0” and a luminance value greater than the threshold valueinto “1”. Then, the calculator 53F may compare the binarized first andsecond image data D1 and D2 to acquire the relative position.

Although the above description concerns a case where fluctuations arepresent in Y-direction (orthogonal direction 20), the peak position mayoccur at a position displaced in X-direction (conveyance direction 10)when there is a fluctuation in the X direction.

Alternatively, the calculator 53F can adapt a different method toacquire the relative position, the moving amount, or the moving speed.For example, the calculator 53F can adapt so-called pattern matchingprocess to detect the relative position from each of the specklepatterns in the image data.

Thus, the calculator can calculate the displacement amount ΔD(n) of theweb 120 in the orthogonal direction 20 and the conveyance direction 10through the correlation operation. The displacement amount ΔD(n)indicates how much the web 120 (object) is deviated from thepredetermined position in the orthogonal direction 20 and the conveyancedirection 10.

[Controller]

The configuration of the controller 520 (in FIG. 2), serving as thecontroller to control the head unit 210, is described below.

FIG. 11 is a schematic block diagram of a controller according to thepresent disclosure. For example, the controller 520 includes a host 71(or a higher-order device), such as an information processing apparatus,and an apparatus-side controller 72. In the illustrated example, thecontroller 520 controls the apparatus-side controller 72 to form animage on a web 120 (object) according to image data and control datainput from the host 71.

Examples of the host 71 include a client computer (personal computer orPC) and a server. The apparatus-side controller 72 includes a printercontroller 72C and a printer engine 72E.

The printer controller 72C governs operation of the printer engine 72E.The printer controller 72C transmits and receives the control data toand from the host 71 via a control line 70LC. The printer controller 72Cfurther transmits and receives the control data to and from the printerengine 72E via a control line 72LC. Through such data transmission andreception, the control data indicating printing conditions and the likeare input to the printer controller 72C. The printer controller 72Cstores the printing conditions, for example, in a register. The printercontroller 72C then controls the printer engine 72E according to thecontrol data to form an image based on print job data, that is, thecontrol data.

The printer controller 72C includes a CPU 72Cp, a print control device72Cc, and a memory 72Cm. The CPU 72Cp and the print control device 72Ccare connected to each other via a bus 72Cb to communicate with eachother. The bus 72Cb is connected to the control line 70LC via acommunication interface (I/F) or the like.

The CPU 72Cp controls the entire apparatus-side controller 72 based on acontrol program and the like. That is, the CPU 72Cp is a processor aswell as a controller.

The print control device 72Cc transmits and receives data indicating acommand or status to and from the printer engine 72E, based on thecontrol data transmitted from the host 71. Thus, the print controldevice 72Cc controls the printer engine 72E.

To the printer engine 72E, a plurality of data lines, namely, data linesTOLD-C, TOLD-M, TOLD-Y, and TOLD-K are connected. The printer engine 72Ereceives the image data from the host 71 via the plurality of data linesTOLD-C, TOLD-M, TOLD-Y, and TOLD-K. Then, the printer engine 72Eperforms image formation of respective colors, controlled by the printercontroller 72C.

The printer engine 72E includes a plurality of data management devices,namely, data management devices 72EC, 72EM, 72EY, and 72EK. The printerengine 72E includes an image output 72Ei and a conveyance controller72Ec.

FIG. 12 is a block diagram of a configuration of the data managementdevice 72EC. For example, the plurality of data management devices 72EC,72EM, 72EY, and 72EK may have an identical configuration, and the datamanagement device 72EC is described below as a representative. Redundantdescriptions are omitted.

The data management device 72EC includes a logic circuit 72EC1 and amemory 72ECm. As illustrated in FIG. 11, the logic circuit 72EC1 isconnected to the host 71 via the data line TOLD-C. The logic circuit72EC1 is connected to the print control device 72Cc via the control line72LC. The logic circuit 72EC1 is implemented by, for example, anapplication specific integrated circuit (ASIC) or a programmable logicdevice (PLD).

According to a control signal input from the printer controller 72C, thelogic circuit 72EC1 stores, in the memory 72ECm, the image data inputfrom the host 71.

According to a control signal input from the printer controller 72C, thelogic circuit 72EC1 retrieves, from the memory 72ECm, cyan image dataIc. The logic circuit 72EC1 then transmits the cyan image data Ic to theimage output 72Ei.

The memory 72ECm preferably has a capacity for storing image dataextending about three pages. With the capacity for storing image dataextending about three pages, the memory 72ECm can store the image datainput from the host 71, image data currently used in image formation,and image data for subsequent image formation.

FIG. 13 is a block diagram of a configuration of the image output 72Ei.In FIG. 13, the image output 72Ei includes an output control device72Eic and the head units 210K, 210Y, 210M, and 210C for respectivecolors of black, yellow, magenta, and cyan.

The output control device 72Eic outputs the image data for respectivecolors to the head units 210 for respective colors, respectively. Thatis, the output control device 72Eic controls the head units 210 forrespective colors based on the image data input to the output controldevice 72Eic.

The output control device 72Eic controls the plurality of head units 210either simultaneously or individually. Thus, the output control device72Eic receives timing commands and changes the timings at which the headunits 210 discharge respective color inks. The output control device72Eic may control one or more of the head units 210 based on the controlsignal input from the printer controller 72C (illustrated in FIG. 11).Alternatively, the output control device 72Eic may control one or moreof the head units 210 based on user instructions, for example.

In the example illustrated in FIG. 11, the apparatus-side controller 72has different routes including a route for inputting the image data fromthe host 71 and a route for transmission and reception of the controldata between the host 71 and the apparatus-side controller 72.

The conveyance controller 72Ec (in FIG. 11) includes a motor, amechanism, and a driver for conveying the web 120. For example, theconveyance controller 72Ec controls the motor coupled to the rollers toconvey the web 120.

[Example of Position Detection]

FIG. 14 is a timing chart of detecting the position of the web 120(object) performed by the image forming apparatus 110 according to thepresent disclosure.

The calculator 53F calculates an amount of displacement of the web 120(object) in the conveyance direction 10 and the orthogonal direction 20based on sensor data provided from the sensor devices SEN. Specifically,the calculator 53F outputs the result of calculated amount ofdisplacement based on a first sensor data SD1 and a second sensor dataSD2. In FIG. 14, an upstream sensor device SEN outputs a first sensordata SD1, and a downstream sensor device SEN outputs a second sensordata SD2.

The amount of displacement is calculated for each of the head units 210,for example. An example of calculation of the displacement of the web120 for adjustment of the head unit 210K for black is described below.Here, the second sensor device SEN2 outputs the first sensor data SD1,and the sensor device SENK for black outputs the second sensor data SD2.

When “L2” represents the distance (interval) between the second sensordevice SEN2 and the sensor device SENK for black, “V” represents aconveyance speed detected based of the sensor data, and “T2” representsa conveyance time for conveying the web 120 (object) from the secondsensor device SEN2 to the sensor device SENK for black. Then, theconveyance time “T2” is calculated as “T2=L2/V”.

Further, when “A” represents a sampling interval of the sensor devicesSEN and “n” represents the number of times of sampling performed whilethe web 120 travels from the sensor device SENK to the sensor deviceSENC, the number of times of sampling “n” is calculated as “n=T2/A”.

The calculation result is referred to as a displacement “AX”. Forexample, when a detection cycle is “0”, the displacement ΔX of the web120 is calculated by comparing the first sensor data SD1 before thetravel time “T2” with the second sensor data SD2 at the detection cycle“0”. Specifically, the displacement ΔX is calculated as“ΔX=X2(0)−X1(n)”.

Next, the head moving unit 57F controls the first actuator AC1 (seeFIGS. 3 and 7) to move the head unit 210K for black in the orthogonaldirection 20 to compensate for the displacement ΔX. With this operation,the image forming apparatus 110 can compensate for the displacementamount ΔX and accurately form an image on the web 120 (object) even whenthe position of the web 120 (object) changes in the orthogonal direction20. Further, the displacement ΔX is calculated based on two sensor dataSD1 and SD2 detected by sensor devices SEN2 and SENK, respectively.Then, the displacement ΔX may be calculated without integrating positiondata of each sensor devices SEN. Thus, this operation can reduceaccumulation of detection errors by each of the sensor devices SEN.

The sensor device SEN to generate the sensor data SD1 is not limited tothe sensor device SEN2 disposed next to and upstream from the sensordevice SENK for the head unit 210K to be moved. That is, the sensor dataSD1 may be generated by any of the sensor devices SEN disposed upstreamfrom the head unit 210 to be moved. For example, any one of the secondsensor device SEN2 and the sensor devices SENK and SENC can generate thefirst sensor data SD1 to calculate the displacement ΔX of the web 120for adjusting the head unit 210Y for yellow to be moved.

On the other hand, the second sensor data SD2 is preferably generated bythe sensor device SEN closest to the head unit 210 to be moved.

Alternatively, the displacement ΔX of the web 120 (object) may becalculated based on three or more detection results (sensor data).

The image forming apparatus 110 controls to move the head unit 210 anddischarge the liquid onto the web 120 and form an image on the web 120according to the displacement ΔX of the web 120 calculated based on aplurality of sensor data SD1 and SD2. Further, the image formingapparatus 110 can accurately discharge and land the liquid (ink) ontothe web 120 (object) in the conveyance direction 10 by controlling thedischarge timing of the head units 210 according to the displacement ΔXin the conveyance direction 10.

[Control of Process Timing]

FIG. 15 is a timing chart of a process timing of the image formingapparatus 110 according to the present disclosure. In FIG. 15, a firsttiming T1 is a detection timing at which the sensor device SENK forblack performs detection. Similarly, a second timing T2 is a processtiming at which the head unit 210K for black discharges black liquid(ink). Further, a third timing T3 is a detection timing at which thesensor device SENC for cyan performs detection.

As illustrated in FIG. 2, the sensor device SENC for cyan is disposedbetween the head unit 210K for black and the head unit 210C for cyan.Further, a fourth timing T4 is a process timing at which the head unit210C for cyan discharges cyan liquid (ink). A fifth timing T5 is theprocessing timing at which the head unit 210C for cyan discharges thecyan liquid (ink) after adjustment of the adjusting unit 55F accordingto the detection results of the sensor device SENK and the sensor deviceSENC.

In this example, the position at which the sensor device SENC for cyanperforms detection is hereinafter simply referred to as “detectionposition”. Following assumption is made in the following example. Thedetection position is at a “distance D” from a position where the inkdischarged from the head unit 210C for cyan lands. An installationinterval between each sensor devices SEN is identical to an installationinterval (relative distance L) between each head units 210. The web 120moves at an ideal moving speed V. The ideal moving speed V is stored inthe printer controller 72C (see FIG. 11).

First, the sensor device SENK for black acquires image data at a firsttiming T1, which is a timing earlier by D/V than the second timing T2 atwhich the head unit 210K for black discharges the black liquid (ink). InFIG. 15, the image data acquired at the first timing T1 is indicated bya first image signal “PA”. This image data corresponds to the image dataD1(n) acquired at the “position A” by the image acquiring unit 52A asillustrated in FIG. 7. Next, the image forming apparatus 110 turns “ON”a first signal SIG1 to control the head unit 210K to discharge the blackliquid at the second timing T2.

Next, the imaging acquiring unit 52B of the image forming apparatus 110acquires the image data at the third timing T3. In FIG. 15, the imagedata acquired at the third timing T3 is indicated by the second imagesignal PB, and this image data corresponds to the image data D2 (n)acquired at the “position B” as illustrated in FIG. 7. Next, thecalculator 53F of the image forming apparatus 110 performscross-correlation calculation on the image data D1 (n) and D2 (n). Thus,the calculator 53F of the image forming apparatus 110 can calculate thedisplacement amount ΔD(0). Then, the adjusting unit 55F controls thetiming of turn “ON” the second signal SIG2 based on the displacementamount ΔD(0). The second signal SIG2 is the timing at which the headunit 210C for cyan discharges cyan liquid (ink)

When no thermal expansion occurs in a roller and no slippage occursbetween the roller and the web 120, that is, in a so-called in an idealstate, it takes time “L/V” to convey a predetermined position of the web120 for the relative distance L at the moving speed V for the imageforming apparatus 110.

Thus, an “imaging cycle T” in which each imaging units 16A and 16Bperforms imaging (capturing) is set to be “imaging cycle T=imaging timedifference=relative distance L/moving speed V” as an initial setting,for example. In FIG. 7, the optical sensors OS of the sensor device SENKfor black and the sensor device SENC for cyan are installed at intervalsof the relative distance L. In the ideal state, the predeterminedposition of the web 120 detected by the sensor device SENK for black isconveyed to the detection position of the sensor device SENC for cyanafter the time “L/V”.

Conversely, practically, the web 120 is often not conveyed with an idealmoving amount because of occurrence of the thermal expansion in therollers and the slippage between the rollers and the web 120. In amethod of the correlation calculation, when the relation of “imagingcycle T=relative distance L/movement speed V” is set, a time differencebetween the timing at which the image data D1(n) is imaged by the sensordevice SENK for black and the timing at which the image data D2(n) isimaged by the sensor device SENC for cyan is calculated by “L/V”. Inthis way, the image forming apparatus 110 may calculate the displacementamount ΔD(0) by using a result of calculation of “L/V” as the “imagingcycle T”. A calculation of the displacement amount ΔD(0) is describedbelow using the third timing T3 in FIG. 15 as an example.

At the third timing T3, the calculator 53F of the image formingapparatus 110 calculates the displacement amount ΔD (0) that is anexample of the second distance. Then, the adjusting unit 55F of theimage forming apparatus 110 controls the head unit 210C for cyan tochange the process timing of discharging the cyan liquid (ink), that is,the timing of turning “ON” the second signal SIG2, based on the distanceD, the displacement amount ΔD(0), and the moving speed V of the web 120.

First, the fourth timing T4 is determined based on the ideal state, thatis, “L/V”. Practically, the ink discharge position PC (see FIG. 2), onwhich the cyan liquid is discharged, is at a position displaced from theink discharge position PC of the head unit 210C for cyan by thedisplacement amount ΔD(0) because of the thermal expansion of the rollerand the like. Thus, it takes time “ΔD(0)/V” to convey the web 120 fromthe ink discharge position PC of the head unit 210C before adjustment tothe ink discharge position PC of the head unit 210C after adjustment.Thus, the adjusting unit 55F of the image forming apparatus 110 controlsthe head unit 210C for cyan to change the process timing from the fourthtiming T4 to the fifth timing T5 so that the liquid can be dischargedonto the position adjusted by the displacement amount ΔD(0) from theideal position.

The image forming apparatus 110 shifts the timing of turning “ON” thesecond signal SIG2 from the fourth timing T4 to the fifth timing T5 by“ΔD(0)/V”. Thus, the image forming apparatus 110 changes the timing ofdischarging the liquid from the head unit 210 based on the displacementamount ΔD(0), the distance D, and the moving speed V, even if thethermal expansion occurs in the rollers and the like. Thus, the imageforming apparatus 110 can improve the accuracy of the ink dischargeposition PC of the cyan liquid onto the web 120 in the conveyancedirection 10.

Besides, an ideal moving speed may be preset for each mode in thecontroller 520 of the image forming apparatus 110. The ideal movingspeed is obtained in a state without thermal expansion or the like.

Although the above example describes changing and determining theprocess timing, the image forming apparatus 110 may directly calculatethe timing of discharging the liquid by the head unit 210 based on thedisplacement amount ΔD(0), the moving speed “V”, and the distance “D”.

[Overall Process]

FIG. 16 is a flowchart of a process of adjustment of a light quantity bythe detection device SEN according to the present disclosure. In thisflowchart, an example in which the light quantity is adjusted using thesensor device SENK for black and the sensor device SENC for cyan isdescribed.

In step SP01, the conveyance controller 72Ec (see FIG. 11) of the imageforming apparatus 110 conveys the web 120 (object) to a detectableposition where the sensor device SENK for black can detect the web 120.Preferably, the conveyance controller 72Ec conveys the web 120 to thedetectable position and stops a conveyance of the web 120 at thedetectable position to maximize difference. However, the controller 520may detect the web 120 by the sensor device SENK for black whileconveying the web 120 without stopping.

In step SP02, the control circuit 52 (see FIG. 5) of the sensor deviceSENK for black initializes the light quantity of the laser light sourceLG of the sensor device SENK for black under the control of thecontroller 520. For example, the control circuit 52 performs processessuch as setting the light quantity irradiated by the laser light sourceLG to an initial value. Here, the initial value is set in advance by theuser in the image forming apparatus 110. In an initialization process instep SP02, other set values and the like of the image forming apparatus110 may be initialized. Hereinafter, an example is described in whichthe initial value of the light quantity is set to “30 mW” by theinitialization process.

In step SP03, the control circuit 52 controls the laser light source LGand irradiates the web 120 (object) with light under the control of thecontroller 520. The light quantity irradiated by the laser light sourceLG is set by the initialization process (step SP02) or a process ofadjustment of the light quantity (step SP07). Thus, the laser lightsource LG irradiates the web 120 (object) with light by the lightquantity of 30 mW when the process is first reached to the step SP03.

In step SP04, the optical sensor OS of the sensor device SENK for blackcaptures (images) the web 120 (object). In this manner, the opticalsensor OS can generate image data indicating the speckle patternappeared on the web 120 (object) when the sensor device SEN captures theweb 120 (object). Further, the image data generated in this manner isused for controlling an imaging (capturing) condition of the lightirradiated in step SP03.

In step SP05, the controller 520 calculates a difference between amaximum pixel value and an average value. The maximum pixel value is apixel value having the largest value among the pixel values indicated bypixels distributed in a predetermined area in the image data generatedin step SP04. The average value is a value obtained by averaging theother pixel values excluding the pixel having the maximum pixel value inthe predetermined area of the image data. For example, the controller520 of the image forming apparatus 110 first searches the maximum pixelvalue in the predetermined area in the image data. Next, the controller520 calculates the average value of the other pixel values excluding themaximum pixel value.

Then, the controller 520 calculates a difference ΔPw between the maximumpixel value and the average value. Further, the controller 520 storesthe difference ΔPw between the calculated maximum pixel value and theaverage value in the memory in the controller 520, for example, thememory 72Cm (see FIG. 11) in association with the emitted lightquantity. The predetermined area is set in advance by the user in theimage forming apparatus 110. Further, the image data generated in stepSP04 is also stored in the memory 72Cm (see FIG. 12) in association withthe emitted light quantity.

In step SP06, the controller 520 determines whether the emitted lightquantity is equal to or above the upper limit value. Specifically, theupper limit value is set to “105 mW” for example. The upper limit valueis an example of a predetermined value.

When the light quantity is not equal to or above the upper limit value(NO in step SP06), the controller 520 proceeds to step SP07.

In step SP07, the controller 520 controls the control circuit 52 (seeFIG. 5) to increase the light quantity emitted from the laser lightsource LG. Specifically, when the light quantity is set to be raised for“+5 mW” beforehand, the controller 520 adjusts the light quantity, theinitial value of which is “30 mW”, to be “35 mW”.

This process is repeated until the emitted light quantity becomes equalto or above the upper limit value in step SP06. Thus, the controller 520increases the light quantity until the light quantity reaches the upperlimit value (“105 mW” in this example) and stores the difference ΔPwbetween the maximum pixel value and the average value in associationwith the emitted light quantity in the memory 72Cm of the controller 520(apparatus-side controller 72). Thus, the controller 520 stores thedifference ΔPw in the memory 72Cm each time of adjustment of the lightquantity.

Next, when the controller 520 determines that the light quantity isequal to or above the upper limit value (YES in step SP06), thecontroller 520 proceeds to step SP08.

In step SP08, the controller 520 compares a plurality of differences APwstored in the memory 72Cm and specifies the difference ΔPw having thelargest value (hereinafter referred to as “maximum difference”). Next,the controller 520 adjusts the light quantity to be equal to the lightquantity associated with the maximum difference.

The larger the difference ΔPw is, the larger the difference between themaximum value and the average value becomes. A strength of thecorrelation peak tends to be large in the image data having largerdifference ΔPw when the correlation is calculated. Thus, a clearcorrelation is easily obtained in the image data having largerdifference ΔPw. Thus, the image forming apparatus 110 adjusts the lightquantity of the laser light source SG to be the light quantityassociated with the maximum difference. Thus, the image formingapparatus 110 can capture (image) the image data that facilitatessearching for correlation peaks obtained by correlation calculation.

Next, in step SP09, the conveyance controller 72Ec conveys the web 120to the position of the sensor device SENC for cyan.

In step SP10, the controller 520 controls the control circuit 52 of thesensor device SENC for cyan to set the light quantity to besubstantially the same as the emitted light quantity of the sensordevice SENK for black.

In step SP11, the optical sensor OS of the sensor device SENC for cyancan capture (image) image data indicating the speckle pattern of theobject.

In step SP12, the controller 520 performs correlation calculation andthe like. Specifically, the controller 520 performs the correlationcalculation between the image data corresponding to set light quantityand the image data captured in step SP11, among the image data stored inthe memory 72Cm in association with the light quantity in step SP05. Forexample, the controller 520 performs a correlation calculation asillustrated in FIG. 7.

In step SP13, the controller 520 determines whether the strength of thecorrelation peak is equal to or above a specified value. The specifiedvalue is set in advance by the user in the image forming apparatus 110.The controller 520 determines whether the result of the correlationcalculation is obtained that allows accurate searching of thecorrelation peak. Specifically, the larger the strength of thecorrelation peak, the more the correlation peak is likely to beaccurately searched. Thus, the controller 520 compares the strength ofthe correlation peak obtained by the correlation calculation in stepSP12 with the specified value, and determines whether the strength ofthe correlation peak is equal to or above the specified value.

The controller 520 may determine whether the correlation peak isappeared within the predetermined area.

Next, when the controller 520 determines that the strength of thecorrelation peak is equal to or above the specified value (YES in stepSP13), the controller 520 ends the process of adjusting the lightquantity. Conversely, if the controller 520 determines that theintensity of the correlation peak is less than the specified value (NOin step SP13), the controller 520 determines whether a number of currentadjustment equals the predetermined number of adjustment (SP14). Whenthe number of current adjustment equals the predetermined number ofadjustments (YES in step SP14), a control panel provided in the imageforming apparatus 110 notifies an error (step SP16) because the laserlight source LG is defective, for example.

When the number of current adjustment does not reach the predeterminednumber of adjustment (NO in step SP14), the controller 520 incrementsthe number of adjustments by one (t1+1) (step SP15) and proceeds to stepSP02. The user may arbitrarily set the predetermined number ofadjustment for determining whether to notify the error. However, it ispreferable to set the predetermined number of adjustment to three tomaintain a process speed.

Then, the controller 520 calculates the relative position, the movingspeed, the moving amount, or the combination above of the web 120 usingthe adjusted light quantity and controls the position of the head unit210 and the timing of discharging the liquid by the head unit 210 untila next process flow illustrated in FIG. 16 is executed.

Comparative Example

FIG. 17 is a schematic cross-sectional view of an image formingapparatus 110A according to a comparative example. As illustrated inFIG. 17, the image forming apparatus 110A of the comparative exampleincludes an encoder 240 on a roller 230 that conveys the web 120. Then,the image forming apparatus 110A of comparative example includes aplurality of liquid discharge head units 210K, 210C, 210M, and 210Y(hereinafter simply referred to as “head unit”) each of which dischargesrespective colors of liquid based on an amount of movement of the web120 measured by the encoder 240.

FIG. 18 is a graph illustrating an example of a displacement amountΔD(n) in ink discharge position (ink landing position) PK, PC, PM and PY(see FIG. 2) when the ink discharged from the head units 210 lands onthe web 120 in a state without adjustment by the image forming apparatus110A of the comparative example.

A first graph G1 represents an actual position of the web 120. A secondgraph G2 represents a position of the web 120 calculated based on theencoder signal from the encoder 240. Thus, when the second graph G2differs from the first graph G1, the actual position of the web 120 andthe calculated position of the web 120 differs in the conveyancedirection 10. Thus, the ink discharge position is likely to deviate.

For example, the displacement amount δ is generated during the head unit210K for black discharging the black liquid. Further, the displacementamount δ may be different for each of the head units 210. Thus, each ofthe displacement amount δ is often different from the displacementamount δ of the head unit 210K for black as illustrated in FIG. 19.

The displacement amount δ is generated, for example, by eccentricity ofthe roller, thermal expansion of the roller, slippage between the web120 and the roller, an elongation and contraction of the web 120, andcombinations of the above. The web 120 is an example of the object or arecording medium,

FIG. 19 is a graph illustrating an influence of the roller eccentricityon displacements in ink discharge position. The graphs illustrated inFIG. 19 indicates one of an example of the influence of the thermalexpansion of the roller, the eccentricity of the roller, and slippagebetween the roller and the web 120 on the displacement in ink dischargeposition. Each graph in FIG. 19 illustrates the displacement amount in avertical axis that represents a difference between the position of theweb 120 calculated based on the encoder signal from the encoder 240 andthe actual position of the web 120. In this example, the roller has anouter diameter of 60 mm and is made of aluminum.

The third graph G3 illustrates the displacement amount when the rollerhas an amount of eccentricity of “0.01 mm”. As indicated by the thirdgraph G3, a period of displacement amount due to eccentricity of theroller is often synchronized with a period of rotation of the roller.Further, the displacement amount due to eccentricity is oftenproportional to an amount of eccentricity. However, the displacementamount is not accumulated in many cases.

A fourth graph G4 indicates the displacement amount when there is aneccentricity and a thermal expansion in the roller. Note that thethermal expansion is under a temperature change of −10° C.

A fifth graph G5 indicates the displacement amount when there is aneccentricity in the roller and a slippage between the web 120 and theroller. In this example, the slippage between the web 120 and the rolleris “0.1 percent”.

There is a case in which the web 120 is tensioned in the conveyancedirection 10 to reduce meandering of the web 120 during conveyance ofthe web 120. This tension on the web 120 may cause expansion andshrinkage of the web 120. The degree of expansion and shrinkage of theweb 120 may vary depending on a thickness, width, amount of liquidapplied to the web 120, or the like.

[Example of Processing Result]

FIG. 20 is a graph illustrating an example of an experimental result foreach object according to a present disclosure. FIG. 20 illustrates theexperimental results when two different types of objects are irradiatedwith light of identical light quantity to generate the image data. InFIG. 20, the horizontal axis indicates a number to specify the pixels ofthe image data. In FIG. 20, the number of the pixels is from “1” to“250” since a total number of pixels is 250. The vertical axis indicatesthe light quantity received by each pixel. With an increase in thereceived light quantity, the pixel value increases in proportion to thereceived light quantity.

FIG. 20 illustrates cases in which the types of the object are a plainpaper TA2 and an offset coated paper TA1. As illustrated in FIG. 20, thereceived light quantity differs according to the type of the object.Specifically, when the material of the object has a high smoothness likethe offset coated paper TA1, the received light quantity tends to belarger than the received light quantity of the plain paper TA2 or thelike.

Even in an imaging condition in which the same light quantity isirradiated on the object, the result of the correlation calculationperformed based on the image data of object differs if the type of theobject is different.

FIG. 21 is a graph illustrating an example of an experiment result whenthe object is a plain paper according to a present disclosure. In FIG.21, the horizontal axis indicates the number to specify the pixels ofthe image data as in FIG. 20. The vertical axis indicates the strengthof correlation. Hereinafter, the strength of correlation in FIGS. 21,22, and 24 illustrate the strength of correlation when a white LED lightsource was used, the light quantity was 30 mW, and a process of abackground noise removal is performed. Also, in FIG. 21, the result ofthe correlation calculation in the orthogonal direction 20 is indicatedby an experiment result “RES11”. Furthermore, in FIG. 21, the result ofthe correlation calculation in the conveyance direction 10 is indicatedby the experiment result “RES12”.

FIG. 22 is a graph illustrating an example of an experimental resultwhen the object is a coated paper according to a present disclosure. Thehorizontal axis and the vertical axis are the same as in FIG. 21. InFIG. 22, the result of the correlation calculation in the orthogonaldirection 20 is indicated by an experiment result “RES21”. In FIG. 22,the result of the correlation operation in the conveyance direction 10is indicated by an experiment result “RES22”.

As illustrated in FIGS. 21 and 22, when comparing FIG. 21 and FIG. 22,the strength of the correlation peak differs even under the same imaging(capturing) condition. Specifically, the light quantities received inthe experiment results RES11 and RES12 are small in FIG. 20. Thus, asensitivity when the correlation calculation is performed tends to below. That is, the strength of the correlation peak becomes small in theexperiment results RES11 and RES12 since the difference between thestrength of correlation at the peak and the strength of correlationother than the peak is small.

Further, when comparing a waveform between FIG. 21 and FIG. 22, there isdistortion in the waveform of the experiment results RES11 and RES12 inFIG. 21. Thus, a detection error by repetition (repetitive detectionerror) tends to increase in the experiment results RES11 and RES12. Therepetitive detection error is a variation in measured values when thevalues are repeatedly measured at the same position. Further, thedifference between the maximum pixel value and the average pixel valuetends to be small. Thus, a difference of distribution of the strength ofcorrelation between the peak position and the background is small. Thus,it is likely that the peak position may not be specified in thedistribution of the strength of correlation.

As illustrated in FIG. 22, the light quantity received in the experimentresults RES21 and RES22 are larger than the light quantity received inthe experiment results RES11 and RES12 in FIG. 21. Thus, the sensitivitywhen correlation calculation is performed tends to be high in theexperiment results RES21 and RES22. The difference between the strengthof correlation at the peak and the strength of correlation other thanthe peak is large in the experiment results RES21 and RES22.

Thus, the strength of the correlation peak becomes large in theexperiment results RES21 and RES22. Thus, the detection error byrepetition (repetitive detection error) tends to be small in theexperiment results RES21 and RES22 because the waveform has a shapeclose to a normal distribution. Further, a margin for erroneousdetection tends to be sufficiently large since the difference betweenthe maximum pixel value and the average pixel value tends to be large.

The above experiment results are obtained by performing the process fromstep SP03 to step SP05 in FIG. 16, for example.

Thus, as illustrated in FIG. 22, if the difference between the peakvalue and the other values is large, the strength of the correlationpeak becomes large. Thus, an accurate detection result can be easilyobtained. Conversely, the strength of the correlation peak tends to besmall in a state as illustrated in FIG. 21. Thus, the detector 600adjusts the light quantity by the step SP0T in FIG. 16, for example, asdescribed below.

FIG. 23 is a graph illustrating a result of an adjustment by thedetector 600 according to the present disclosure. The horizontal axisand the vertical axis are the same as in FIG. 20. Hereinafter, it isassumed that the type of the object is plain paper.

An experiment result ADB before the adjustment is performed isillustrated in FIG. 23. The experiment result ADB is obtained under animaging condition in which the web 120 is irradiated with a laser light,a light quantity of which is set as initialized condition, for example.Thus, the experiment result ADB is obtained (captured) under the imagingcondition similar to the imaging condition in FIG. 20 for plain paperTA1.

Further, an experiment result ADA after the adjustment is performed isillustrated in FIG. 23. The experiment result ADA is obtained under animaging condition in which the web 120 is irradiated with a laser light,a light quantity of which is adjusted such as by the steps SP08 and SP10as illustrated in FIG. 16. As illustrated in FIG. 23, when theadjustment is performed, a difference DIF between a maximum pixel valuePXM and the average pixel value PXAV of the experiment result ADAbecomes larger than the difference DIF of the experiment result ADB.

Specifically, as illustrated in FIG. 23, a point having the largestpixel value among the pixel values is the peak point PMX. The averagepixel value PXAV is a value obtained by averaging the respective pixelvalues of the pixels other than the pixel of the peak point PMX.

Thus, the detector 600 preferably adjusts the imaging condition (lightquantity) by changing the imaging condition so that the difference DIFbecomes the maximum. The maximum difference DIF is chosen among aplurality of differences DIF calculated based on the image data capturedunder each imaging conditions. In this way, the detector 600 can set theimaging condition in which the difference DIF becomes the largest amongthe imaging conditions settable by the detector 600 by the adjustment.The detector 600 may set the imaging condition such that the differenceDIF equals to 80% or more of the largest value of the difference DIF.

Results of the adjustment as described below can be obtained by theabove described correlation calculation.

FIG. 24 is a graph illustrating a result of an adjustment by thedetector 600 according to the present disclosure. The horizontal axisand the vertical axis are the same as in FIG. 21. FIG. 24 illustratesthe result of performing the correlation calculation on the capturedimage data after the adjustment as illustrated in FIG. 23.

As in FIG. 21 and the like, FIG. 24 illustrates the result of thecorrelation calculation in the orthogonal direction 20 indicated by anexperiment result “RES31”. Further, in FIG. 24, the result of thecorrelation operation in the conveyance direction 10 is indicated by anexperiment result “RES32”.

The detector 600 can easily search correlation peaks if an experimentresult is similar to the experiment results RES31 and RES32. Thewaveforms illustrated in FIG. 24 have a shape close to the normaldistribution. Thus, the repetitive detection error tends to be small inthe experiment results RES31 and RES32. Further, a margin for erroneousdetection tends to be sufficiently large since the difference betweenthe maximum pixel value and the average pixel value tends to be large.

If the light quantity irradiated to the web 120 (object) is too large,the received light quantity may reach the upper limit value in somecases. In such a case, the difference DIF may become small. Thus, it ispreferable to set the upper limit value of the light quantity forirradiation.

FIG. 25 is a flowchart of the process of adjustment of the lightquantity according to the present disclosure. Here, the “process” is aprocess to discharge the liquid. Referring to FIGS. 5 and 25, thecontroller 520 determines whether an object (web 120, for example) isthe object whose light quantity has been adjusted (S01). Hereinafter,the object whose light quantity has been adjusted is simply referred toas “adjusted object”. The controller 520 determines whether the objectis the adjusted object by previously storing a type of the adjustedobject in the past in the memory 521 in the controller 520 and comparesthe stored adjusted object and the type of the object input by the user.

If the object is the adjusted object in the past (YES in S01), thecontroller 520 transmits data of light quantity associated with the typeof the adjusted object stored in the memory 521 in the controller 520 tothe control circuit 52. Then, the control circuit 52 sets the lightquantity based on the data of the light quantity transmitted from thecontroller 520 (S02). If the object is not the adjusted object in thepast (NO in S01), the controller 520 performs the process of acquiringthe light quantity as described in FIG. 16 (S03).

Then, the control circuit 52 sets the light quantity acquired by theprocess of acquiring the light quantity as described in FIG. 16 (S04).Then, the image forming apparatus 110 executes the process ofdischarging the liquid onto the web 120 (hereinafter, simply referred toas “discharge process”) while conveying the object after the lightquantity is determined in S02 or S04 (505).

The discharge process includes a calculation of the relative position,the moving speed, the moving amount, or the combination above of the web120 using the adjusted light quantity and a control of the position ofthe head unit 210 and the timing of discharging the liquid by the headunit 210. The calculator 53F (see FIGS. 7 and 8) performs thecorrelation calculation to calculate the moving amount of the web 120 inthe conveyance direction (S06) during executing the above describedprocess.

The controller controls to drive the actuators (AC1 through AC4 in FIG.3) in step S07 and controls the process timing (S08) based on thecalculated moving amount. The controller 520 determines whether theprocess of the image forming apparatus 110 has ended after thecontroller 520 controls to drive the actuators AC and controls theprocessing timing in step S09. If the discharge process is not completed(S09, NO), the present process returns to step S06. If the abovedescribed discharge process completes (S09, YES), the present dischargeprocess ends.

The step S07 and S08 are executed in parallel in FIG. 16. However, thestep S07 and S08 may be executed in series or executed alternately.

[Variation]

FIG. 26 is a schematic view of a variation of the image formingapparatus 110 according to the present disclosure. The configurationillustrated in FIG. 26 differs from the configuration illustrated inFIG. 2 regarding the locations of the first support (e.g., theconveyance roller CR1C in FIG. 2) and the second support (e.g., theconveyance roller CR2K in FIG. 2). The first support and the secondsupport may be implemented by a first roller RL1, a second roller RL2, athird roller RL3, a fourth roller RL4, and a fifth roller RL5. That is,the first support and the second support may commonly be used. Notethat, the first support and the second support may also serve as rollersor may serve as curved plates.

Second Embodiment

In the flow illustrated in FIG. 16, the light quantity is adjusted usingthe laser light source LG of the black sensor device SENK, and the laserlight source LG of the cyan sensor device SENC is matched with the lightquantity of the laser light source LG of the black sensor device SENK.However, the light quantity may be individually adjusted for each laserlight source LG so that the difference ΔPw detected by each sensordevice SEN is maximized, respectively.

The light source LG is not limited to laser light sources but can belight emitting diodes (LED) or the like. For example, the light sourcemay be an LED (Light Emitting Diode) or an organic EL(Electro-Luminescence) or the like. Depending on the light source, thepattern appeared on the web 120 (object) need not be a speckle pattern.

Further, the light source may be a light source having a singlewavelength or a light source having a broad wavelength.

In the above embodiment, an image forming apparatus 110 that performsimage formation using four color of head units 210 of black, cyan,magenta, and yellow has been described as an example. However, the imageforming apparatus 110 may include a plurality of, for example, headunits 210K for black to perform image formation.

Further, the object is not limited to a recording medium such as paper.The object is, for example, a material to which a liquid can adhere orthe like. Examples of the material on which liquid can be adheredinclude any materials on which liquid can be adhered even temporarily,such as paper, thread, fiber, fabric, leather, metal, plastic, glass,wood, ceramic, and combination of the above.

The present embodiment may be realized by one image forming apparatus110 or may be realized by two or more image forming apparatuses 110. Forexample, the head unit 210K for black and the head unit 210C for cyanare disposed inside a first casing, and the head unit 210M for magentaand the head unit 210Y for yellow are disposed inside a second casing.In this example, the image forming apparatus 110 is implemented as asystem including two devices. In addition, each process described abovemay be performed in parallel, redundantly, or distributedly by aplurality of information processing apparatuses such as calculator 53Fin the detector 600.

Further, the liquid used in the present disclosure is not limited toink, and other types of recording liquid or fixation processing liquidor the like may be used. That is, an apparatus that discharges liquid(ink) according to the present disclosure may be applied to an apparatusthat discharges a liquid of a type other than ink.

Therefore, an apparatus according to the present disclosure is notlimited to an apparatus that performs an image forming process. Forexample, the object to be formed may be a three-dimensional object orthe like.

Third Embodiment: Reading Apparatus

FIG. 27 is a schematic top view of a reading apparatus according to thethird embodiment of the present disclosure. In the first embodiment andthe second embodiment described above, an example of the image formingapparatus 110 including the head unit 210 that discharges the liquid andthe conveyor including the nip roller pairs NR1 and NR2 and the roller230 (see FIG. 2). However, the head unit may be a reading unit (scanner)to perform a reading process. In this case, the conveyor (the nip rollerpairs NR1 and NR2 and the roller 230 in FIG. 2, for example) functionsas a conveyor for the reading apparatus.

The reading apparatus 1 reads an image on the web 120 by each of thehead units HD1 and HD2 at different position along a conveyance path.The web 120 is conveyed by the conveyor including nip roller pairs NR1and NR2 and a roller 230. The head units HD1 and HD2 include readingheads CIS1 and CIS2, respectively. The reading heads CIS1 and CIS2include a group of a contact image sensors (CIS), respectively. In thepresent embodiment, the reading heads CIS1 and CIS2 perform a readingprocess at reading positions PK and PC as illustrated in FIG. 28.

The head units HD1 and HD2 include one or more reading heads disposedalong the orthogonal direction 20, respectively. For example, asillustrated in FIG. 27, the reading apparatus 1 includes two head unitsHD1 and HD2. Although the reading apparatus in FIG. 27 includes two headunits HD1 and HD2, a number of head units in the reading apparatus 1 isnot limited to two, and may be three or more.

As illustrated in the FIG. 27, the head units HD1 and HD2 include one ormore reading heads CIS1 and CIS2, respectively. In FIG. 27, the headunit HD1 includes one reading head CIS1, and the head unit HD2 includesone reading head CIS2. However, the head unit HD1 may include a readinghead CIS3 disposed at a position extending in the orthogonal direction20 of the reading head CIS1 and CIS2 and disposed in staggered mannerwith the reading head CIS1 and the reading head CIS2.

The head units HD1 and HD2 constitute a reading unit, a so-calledscanner. Thus, the head units HD1 and HD2 read an image formed on thesurface of the web 120 and output the image data indicating the readimage or the like. The reading apparatus 1 can generate an imageconnected in the conveyance direction 10 and the orthogonal direction 20by connecting the image data output from each head units HD1 and HD2.

The reading apparatus 1 in FIG. 27 includes support rollers CR1 and CR4that are not provided between the head units HD1 and HD2. However, thenumber of support rollers CR provided between the head units HD1 and HD2is not limited to one. As illustrated in FIG. 28, two or more supportrollers CR2 and CR3 may be provided between the head units HD1 and HD2.

FIG. 28 is an enlarged side view of the reading apparatus 1 illustratedin FIG. 27. As similar to the first embodiment in FIG. 2, two pairs ofnip rollers NR1 and NR2 and rollers 230 are provided on both sides ofthe support rollers CR1 to CR4 sandwiching the head units HD1 and HD2,respectively, as a conveyor. At least one of the nip rollers (NR1 inFIG. 28) among the pair of nip rollers NR1 and NR2 is a driving roller.A driving force is given to the driving roller NR1 by the motor M1 (seeFIG. 28).

Further, the reading apparatus 1 includes a controller CT1 and anactuator controller CT2. The controller CT1 and the actuator controllerCT2 are information processing apparatus. Specifically, the controllerCT1 and the actuator controller CT2 have a hardware configurationincluding a CPU, an electronic circuit, a computing device such as acombination described above, a controller, a memory, an interface, andthe like. The controller CT1 and the actuator controller CT2 may be aplurality of devices.

Installation positions of the sensor devices S1 and S2 are preferablydisposed in a same manner as in FIG. 3.

[Processing Position of Head Unit]

FIG. 29 is a schematic plan view of a process position of the head unitsHD1 and HD2 according to the present disclosure. The reading head CIS1of the head unit HD1 and the reading head CIS2 of the head unit HD2 aredisposed in staggered manner in Y-direction (orthogonal direction 20) asillustrated in FIG. 29. Further, each of the reading heads CIS1 and CIS2includes a plurality of CIS elements arranged in a line in theY-direction and includes a plurality of reading regions R associatedwith each CIS element.

Specifically, the reading head CIS1 of the head unit HD1 reads thereading range SC1 in the Y-direction (orthogonal direction 20) andgenerates read image data. Conversely, the reading head CIS2 of the headunit HD2 reads the reading range SC2 in the Y-direction (orthogonaldirection 20) to generate read image data. As illustrated in FIG. 29,the reading range SC1 and the reading range SC2 partially overlap.Hereinafter, the overlapping range in which the reading range SC1 andthe reading range SC2 overlap is referred to as “overlapping range SC3”.

The head units HD1 and HD2 can read the identical object (web 120) inthe overlapping range SC3. That is, the object (web 120) read by thehead unit HD1 in the overlapping range SC3 is conveyed from upstream todownstream in the conveyance direction 10. Thus, the head unit HD2 canread the same object (web 120) at predetermined time after the head unitHD1 reads the web 120. Since an interval between the head unit HD1 andthe head unit HD2 is known in advance, the reading apparatus 1 cancalculate a timing at which the head unit HD2 reads the object (web 120)read by the head unit HD1 based on the moving speed of the object (web120).

Then, the reading apparatus 1 stores the image data read and generatedby the head units HD1 and HD2 in image storing units 1F51 and 1F52 inthe image processor 1F5 (see FIG. 30). The image processor 1F5 includesan image synthesizer 1F53 that connects each image data in the imagestoring units 1F51 and 1F52 based on the pixels of each image data inthe overlapping range SC3. In this way, the image processor 1F5 of thereading apparatus 1 can connect the image data in the reading range SC1and the reading range SC2 and generate a synthesized data.

The image processor 1F5 includes an image output unit 1F54 to outputsynthesized image data generated by connecting the image data in theimage storing units 1F51 and 1F52. A direction of connecting the imagedata is not limited to the orthogonal direction 20 (Y-direction) and maybe in the conveyance direction 10 (X-direction).

As described above, the reading apparatus 1 can connect read images andgenerate read image of a wide range without connection by the head unitsHD1 and HD2 disposed at different position.

[Functional Configuration]

FIG. 30 is a schematic block diagram of a functional configuration ofthe reading apparatus 1 according to the present disclosure. The readingapparatus 1 in FIG. 30 further includes a controller 1F3. Further, thereading apparatus 1 further includes an image processor 1F5 forprocessing read image data as illustrated in FIG. 30.

The controller 1F3 controls the head units HD1 and HD2. For example, thecontroller 1F3 preferably includes a functional configuration of amovement controller 1F31 and a process timing controller 1F32.

The movement controller 1F31 controls the actuators AC1 and AC2 based onthe displacement amount calculated by the calculator 1F2. For example,the movement controller 1F31 is implemented by the actuator controllerCT2 (see FIG. 28) or the like.

The process timing controller 1F32 controls timing of the readingprocess of the reading heads CIS1 and CIS2 in the head units HD1 andHD2, respectively, based on the displacement amount calculated by acalculator 1F2.

More specifically, the reading apparatus 1 changes process timing tocompensate the displacement amount for “Δx” if the displacement amountin the conveyance direction 10 (X-direction) is “Δx” and the movingspeed of the web 120 is “V”. In this example, the reading apparatus 1changes the process timing of the downstream reading head CIS2 for“ΔT=Δx/V”.

Thus, the reading apparatus 1 changes the process timing (readingtiming) of the reading head CIS2 to be delayed by “ΔT” when the web 120is conveyed with a delay by “Δx”. Thus, the reading apparatus 1 canaccurately perform the reading process in the conveyance direction 10(X-direction).

If the displacement amount in the orthogonal direction 20 (Y-direction)is “Δy”, the reading apparatus 1 moves the head units HD1 and HD2 tocompensate for the displacement amount “Δy”. The reading apparatus 1drives and controls the actuators AC1 and AC2 to move the reading headsCIS1 and CIS2 in the head units HD1 and HD2, respectively, in theorthogonal direction 20. Thus, the reading apparatus 1 can move thereading position of the reading heads CIS1 and CIS2.

In this way, the reading apparatus 1 can accurately perform the processof reading image data (test chart or the like) in the conveyancedirection 10 and the orthogonal direction 20. The reading apparatus 1according to the present disclosure moves the head units HD1 and HD2during the reading process to compensate the displacement amount. Thus,the reading apparatus 1 can accurately perform the reading process bythe head units HD1 and HD2.

Further, as illustrated in FIG. 27, the reading apparatus includes anupstream sensor device S0 and an edge sensor ES0. The upstream sensordevice S0 outputs surface data of web 120 at the most upstream in theX-direction (conveyance direction 10). The edge sensor ES0 outputssurface information of web 120 at an edge of the web 120 in theY-direction (orthogonal direction 20). The upstream sensor device S0 andthe edge sensor ES0 are arranged at an identical position in theX-direction (conveyance direction 10). Thus, the reading apparatus 1according to the present disclosure can detect the displacement amountof the detection position of the speckle pattern from the referenceposition at the upstream sensor device S0.

Thus, the controllers CT1 and CT2 of the reading apparatus 1 cancompensate for the displacement amount by driving and controlling theactuators AC1 and AC2 to move the reading heads CIS1 and CIS2 in thehead units HD1 and HD2, respectively, in the orthogonal direction 20.

The reading apparatus 1 may read a displacement of the edge of the web120 (hereinafter, simply referred to as “edge shift”) during an initialadjustment and correct the reading position of the image of the sensordevice SEN as illustrated in FIGS. 15 and 16 at the time of inspectionperformed by reading a test chart. In this case, the reading apparatus 1calculate the edge shift of the web 120 (object) only at the initialadjustment. Thus, the calculator 53F may calculate only the changeamount (meandering amount) of the web 120 when reading the image dataduring the conveyance of the web 120. Thus, the reading apparatus 1 canread a high-quality image while reducing a load on the controller 520.

As illustrated in FIGS. 17 and 18, the reading apparatus 1 may detectthe edge shift in real time and reflect a detection result of the edgeshift to correct the reading position of the sensor device SEN.

When the edge of the web 120 is detected in real time, the edge shift ofthe web 120 may be calculated by calculating an average of a latestacquired edge shift by a moving average or excluding the acquired edgeshift to which noise is added using the filter. The reading apparatus 1thus calculates the edge shift as described above to avoid an influenceof lack of the edge or noise of web 120 at a timing of sensor samplingof the sensor device SEN during image reading. Thus, the readingapparatus 1 can detect an accurate image reading position.

The reading apparatus 1 detects the edge shift in real time and adjuststhe position of the head units HD1 and HD2 (scanner) at a constant cycleduring image reading. Thus, the reading apparatus 1 can read a higherquality image even if the edge shift occurs on the web 120 duringconveyance of the web 120.

The third embodiment describes an example of the apparatus configuredwith a single unit. The image forming apparatus 110 as illustrated inFIGS. 1 and 2 may include the reading apparatus 1 illustrated in FIG. 30as a part of the image forming apparatus 110.

For example, the reading apparatus 1 according to the present disclosuremay be disposed at the rear stage of the image forming apparatus 110illustrated in FIGS. 2 and 3. Then, the reading apparatus 1 may read atest chart, on which images are formed for inspection to adjust the inkdischarge position (ink landing position) of the liquid onto the web120.

In this case, the head units HD1 and HD2 images (captures) and reads atest pattern to inspect an image. The head units HD1 and HD2 function asa scanner of the reading apparatus 1. The test pattern includes apattern such as a gradation pattern adjusted in density for correctingthe ink discharge position of the liquid onto the web 120.

The reading apparatus 1 according to the present disclosure may includea controller (reading result processor or recording head dischargeposition setting unit, etc.) in addition to a mechanism for readingcolor information of the image by the head units HD1 and HD2 as thescanner.

Further, the image forming apparatus 110 described in the firstembodiment illustrated in FIGS. 2 and 26 may include the readingapparatus 1 described in the third embodiment illustrated in FIGS. 27and 28. The image forming apparatus 110 including the reading apparatus1 can accurately inspect the ink discharge position and form ahigh-quality image reflecting the result of the inspection.

FIGS. 31A and 31B are schematic perspective views of the detectiondevice SEN according to another embodiment of the present disclosure.

The above embodiment describes an example in which correlationcalculation or the like is performed based on image data of a patternoutput from a plurality of sensor devices SENK, SENC, SENM, and SENY.

However, as illustrated in FIGS. 31A and 31B, a single sensor device SENhaving wide visual field angle may capture the same web 120 at differenttimes T1 and T2 and output two image data and perform correlationcalculation on the two-image data. The single sensor device SEN havingwide visual field angle can capture the movement of the speckle pattern(unevenness) 700 in the web 120 within the view of the sensor device SENby capturing the web 120 at different times T1 and T2 if the timedifference between timing T1 and T2 are very short. Thus, the controller520 can detect the relative position, the moving amount, the movingspeed, the edge shift, or a combination the above of the object (web120) between different times T1 and T2.

The above-described image forming apparatus 110 and reading apparatus 1according to the present disclosure may be implemented by a programwhich causes a computer such as the detector 600, for example, toexecute an adjustment method. Therefore, when the adjustment method isexecuted based on the program, the calculator 53F and the controller 520in the computer perform computation and control based on the program inorder to execute each process. Further, the memory of the computerstores data used to execute each process based on a program.

The program may be stored in a computer-readable memory fordistribution. The recording medium may be a medium such as a magnetictape, a flash memory, an optical disk, a magneto-optical disk, or amagnetic disk. Further, the program can be distributed through anelectric communication line.

Further, the present disclosure may adapt a configuration in which aprocessor such as the image forming apparatus 110 or the readingapparatus 1 includes a line-shaped head that moves in the orthogonaldirection 20 to perform some process (image forming, reading, forexample) on a conveyed object. For example, the image forming apparatusmay include head unit that emits laser beam (hereinafter, simplyreferred to as “laser head”) to perform laser patterning on a substrate.The laser heads move in the orthogonal direction 20. Then, the imageforming apparatus may detect the position of the substrate and move thelaser head. Further, the image forming apparatus may include a pluralityof laser heads arranged in a line.

The head units may read an image formed on the object and generate imagedata.

The number of the heads is not necessarily two or more. The imageforming apparatus according to the present disclosure may continue toperform a process (image forming, reading, laser patterning, forexample) at the position on the object identical to the referenceposition.

The present disclosure is not limited to the details of the exemplaryembodiments described above and various modifications and improvementsare possible.

The term “liquid discharge apparatus” used herein is an apparatusincluding the liquid discharge head or the liquid discharge device todischarge liquid by driving the liquid discharge head. The liquiddischarge apparatus may be, for example, an apparatus capable ofdischarging liquid to a material to which liquid can adhere and anapparatus to discharge liquid toward gas or into liquid.

The “liquid discharge apparatus” may include devices to feed, convey,and eject the material on which liquid can adhere. The liquid dischargeapparatus may further include a pretreatment apparatus to coat atreatment liquid onto the material, and a post-treatment apparatus tocoat a treatment liquid onto the material, on which the liquid has beendischarged.

The “liquid discharge apparatus” may be, for example, an image formingapparatus to form an image on a sheet by discharging ink, or a solidfabrication apparatus (three-dimensional fabricating apparatus) todischarge a fabrication liquid to a powder layer in which powdermaterial is formed in layers, to form a solid fabrication object(three-dimensional fabrication object).

In addition, “the liquid discharge apparatus” is not limited to such anapparatus to form and visualize meaningful images, such as letters orfigures, with discharged liquid. For example, the liquid dischargeapparatus may be an apparatus to form meaningless images, such asmeaningless patterns, or fabricate three-dimensional images.

The above-described term “material on which liquid can be adhered”represents a material on which liquid is at least temporarily adhered, amaterial on which liquid is adhered and fixed, or a material into whichliquid is adhered to permeate. Examples of the “medium on which liquidcan be adhered” include recording media, such as paper sheet, recordingpaper, recording sheet of paper, film, and cloth, electronic component,such as electronic substrate and piezoelectric element, and media, suchas powder layer, organ model, and testing cell. The “medium on whichliquid can be adhered” includes any medium on which liquid is adhered,unless particularly limited.

Examples of the material on which liquid can be adhered include anymaterials on which liquid can be adhered even temporarily, such aspaper, thread, fiber, fabric, leather, metal, plastic, glass, wood,ceramic, construction materials (e.g., wall paper or floor material),and cloth textile.

Further, the term “liquid” includes any liquid having a viscosity or asurface tension that can be discharged from the head. However,preferably, the viscosity of the liquid is not greater than 30 mPa·sunder ordinary temperature and ordinary pressure or by heating orcooling.

Examples of the liquid include a solution, a suspension, or an emulsionincluding, for example, a solvent, such as water or an organic solvent,a colorant, such as dye or pigment, a functional material, such as apolymerizable compound, a resin, or a surfactant, a biocompatiblematerial, such as DNA, amino acid, protein, or calcium, and an ediblematerial, such as a natural colorant.

Such a solution, a suspension, or an emulsion can be, e.g., inkjet ink,surface treatment solution, a liquid for forming components ofelectronic element or light-emitting element or a resist pattern ofelectronic circuit, or a material solution for three-dimensionalfabrication.

“The liquid discharge apparatus” may be an apparatus to relatively movea head and a medium on which liquid can be adhered. However, the liquiddischarge apparatus is not limited to such an apparatus. For example,the liquid discharge apparatus may be a serial head apparatus that movesthe head or a line head apparatus that does not move the head.

Examples of the “liquid discharge apparatus” further include a treatmentliquid coating apparatus to discharge a treatment liquid to a sheetsurface to coat the sheet surface with the treatment liquid to reformthe sheet surface and an injection granulation apparatus to discharge acomposition liquid including a raw material dispersed in a solution froma nozzle to mold particles of the raw material.

The “liquid discharge device” is an integrated unit including the liquiddischarge head and a functional parts or mechanisms, and is an assemblyof parts relating to liquid discharge. For example, “the liquiddischarge device” may be a combination of the head with at least one ofa head tank, a carriage, a supply unit, a maintenance unit, and a mainscanner.

Herein, the terms “integrated” or “united” mean fixing the head and thefunctional parts (or mechanism) to each other by fastening, screwing,binding, or engaging and holding one of the head and the functionalparts movably relative to the other. The liquid discharge head may bedetachably attached to the functional parts or mechanisms each other.

The main scanner may be a guide only. The supply unit may be a tube(s)only or a mount part (loading unit) only.

The term “liquid discharge head” used herein is a functional componentto discharge or jet liquid from nozzles. Examples of an energy sourcefor generating energy to discharge liquid include a piezoelectricactuator (a laminated piezoelectric element or a thin-film piezoelectricelement), a thermal actuator that employs a thermoelectric conversionelement, such as a heating resistor (element), and an electrostaticactuator including a diaphragm and opposed electrodes.

In the present embodiment, “sheet” is not limited to paper materially,but includes transparent sheets, cloth, glass, substrates, others towhich ink droplets and other liquids can be attached, and articlesreferred to as a recording medium, a recording sheet, recording paper,etc. The terms “image formation”, “recording”, “printing”, and “imageprinting” used herein may be used synonymously with each another.

The term “ink” is not limited to “ink” in a narrow sense, unlessspecified, but is used as a generic term for any types of liquid usableas targets of image formation such as recording liquid, fixing solution,and liquid. For example, the term “ink” also includes DNA sample,resist, pattern material, resin, and so on.

The term “image” used herein is not limited to a two-dimensional imageand includes, for example, an image applied to a three-dimensionalobject and a three-dimensional object itself formed as athree-dimensionally molded image.

The present embodiment is described in detail using the embodiments. Theembodiments described above are merely an example, and variousmodifications can be made within a range not deviating from the scope ofthe appended claims.

Numerous additional modifications and variations are possible in lightof the above teachings. Such modifications and variations are not to beregarded as a departure from the scope of the present disclosure andappended claims, and all such modifications are intended to be includedwithin the scope of the present disclosure and appended claims.

For example, any one of the above-described operations may be performedin various other ways, for example, in an order different from the onedescribed above.

Each of the functions of the described embodiments may be implemented byone or more processing circuits or circuitry. Processing circuitryincludes a programmed processor, as a processor includes circuitry. Aprocessing circuit also includes devices such as an application specificintegrated circuit (ASIC), digital signal processor (DSP), fieldprogrammable gate array (FPGA), and conventional circuit componentsarranged to perform the recited functions.

What is claimed is:
 1. A detector comprising: a light source configuredto irradiate an object with light; a sensor configured to image a firstpattern and a second pattern formed on the object with the lightirradiated by the light source to generate image data, the first patternand the second pattern imaged by the sensor at different times; and acircuit configured to: control the light source to adjust a lightquantity of the light according to a type of the object, and irradiatethe object with the light quantity adjusted according to the type of theobject; and calculate a relative position of the object between thefirst pattern and the second pattern.
 2. The detector according to claim1, wherein: the circuit is further configured to: calculate a differencebetween a maximum pixel value and an average value in the image data;and adjust the light quantity of the light to control the difference tobe a maximum value; the maximum pixel value is a largest pixel valueamong pixel values of pixels distributed in a predetermined area in thefirst pattern and the second pattern; and the average value is a valueobtained by averaging other pixel values except the maximum pixel value.3. The detector according to claim 2, wherein the circuit is furtherconfigured to: calculate the difference a plurality of times; and adjustthe light quantity of the light to be the light quantity associated withthe maximum value among a plurality of calculated values of thedifference.
 4. The detector according to claim 1, wherein the firstpattern and the second pattern are imaged at different positions.
 5. Thedetector according to claim 1, wherein the first pattern and the secondpattern are formed by the light interfering by an uneven surface of theobject.
 6. An image forming apparatus, comprising: a detector configuredto detect an object; and a head configured to form an image on theobject according to a detection of the detector, wherein the detectorcomprises: a light source configured to irradiate an object with light;a sensor configured to capture a first pattern and a second patternformed on the object with the light irradiated by the light source, thefirst pattern and the second pattern imaged by the sensor at differenttimes; and a circuit configured to: control the light source to adjust alight quantity of the light according to a type of the object, andirradiate the object with the light quantity adjusted according to thetype of the object; calculate a relative position of the object betweenthe first pattern and the second pattern; and control the head to formthe image on the object according the relative position.
 7. The imageforming apparatus according to claim 6, further comprising: a firstsupport disposed upstream of the head in a conveyance direction of theobject, and configured to convey the object to a position opposite thehead; and a second support disposed downstream of the head unit in theconveyance direction of the object, and configured to convey the objectfrom the position opposite the head, wherein the sensor is disposedbetween the first support and the second support.
 8. The image formingapparatus according to claim 7, wherein the sensor is disposed betweenthe first support and the position opposite the head.
 9. The imageforming apparatus according to claim 6, wherein the circuit isconfigured to control a timing at which the head forms the image on theobject according the relative position calculated by the circuit. 10.The image forming apparatus according to claim 6, further comprising anactuator configured to move the head according to the relative positioncalculated by the circuit.
 11. The image forming apparatus according toclaim 10, wherein the actuator is configured to move the head in anorthogonal direction perpendicular to a conveyance direction of theobject.
 12. The image forming apparatus according to claim 6, whereinthe head is configured to discharge liquid onto the object to form theimage on the object.
 13. The image forming apparatus according to claim6, wherein the head is configured to irradiate the object with laserlight to form the image on the object.
 14. A reading apparatus,comprising: a detector configured to detect an object; and a readinghead configured to read an image on the object according to a detectionof the detector, wherein the detector comprises: a light sourceconfigured to irradiate an object with light; a sensor configured toimage a first pattern and a second pattern formed on the object with thelight irradiated by the light source, the first pattern and the secondpattern imaged by the sensor at different times; and a circuitconfigured to: control the light source to adjust a light quantity ofthe light according to a type of the object, and irradiate the objectwith the light quantity adjusted according to the type of the object;calculate a relative position between the first pattern and the secondpattern imaged by the sensor; and control the reading head to read theimage on the object according the relative position.
 15. An adjustmentmethod, comprising: irradiating an object with light; imaging a firstpattern and a second pattern formed on the object with the lightirradiated to the object, the first pattern and the second patternimaged at different times; adjusting a light quantity of the lightaccording to a type of the object; irradiating the object with the lightquantity of the light adjusted according to the type of the object; andcalculating a relative position between the first pattern and the secondpattern.
 16. The image forming apparatus according to claim 6, furthercomprising: a controller configured to determine the light quantity oflight for irradiating the object based on the type of the object, and toexecute a process while conveying the object; and a plurality of sensordevices spaced apart along a conveyance path of the object; wherein afirst one of the sensor devices at a first position along the conveyancepath is configured to irradiate the object with the light having thelight quantity set according to the type of the object, and to image apattern formed on the object with the light at the first position;wherein a second one of the sensor devices at a second position alongthe conveyance path is configured to irradiate the object with the lighthaving the light quantity set according to the type of the object, andto image the pattern formed on the object with the light at the secondposition; wherein the controller is further configured to calculate amoving amount of the object based on the pattern imaged at the firstposition and the pattern imaged at the second position, and to adjust atleast one of a process timing and a process position of the head for theprocess based on the moving amount.
 17. The apparatus according to claim16 wherein: the process comprises a discharge process where the head isconfigured to discharge a recording liquid onto the object.
 18. Theapparatus according to claim 16 wherein: the controller is configured tocontrol an actuator connected to the head to adjust the process positionof the head.
 19. The apparatus according to claim 16, furthercomprising: a first support disposed upstream of the head along theconveyance path, and configured to convey the object to a positionopposite the head; and a second support disposed downstream of the headalong the conveyance path, and configured to convey the object from theposition opposite the head, wherein the second one of the sensor devicesis disposed between the first support and the second support.